Allah, may He be glorified and exalted, says (interpretation of the meaning), "The Messenger has believed in what was revealed to him from his Lord, and so have the believers. All of them have believed in Allah and His angels and His books and His messengers, saying, “We make no distinction between any of His messengers.” And they say, “We hear and we obey. We seek Your forgiveness, our Lord, and to You is the final destination.” (al-Baqarah 2:285) 

Ibn Kathir said, “They believe in all of the prophets and messengers, and the books which were sent down from heaven to Allah’s slaves, the messengers and prophets. They do not differentiate between any of them, believing in some and disbelieving in others; rather all of them, in their view, are truthful, sincere, rational, guided and guided others to the right path, even if some of them abrogated the system of laws of others, by Allah’s leave, until they were all abrogated by the system of law brought by Muhammad (blessings and peace of Allah be upon him), the last of the prophets and messengers, whose system of law will remain valid until the Hour begins.”

In the Sunnah:
The Prophet (blessings and peace of Allah be upon him) said, when Jibril (peace be upon him) asked him about faith, “It is to believe in Allah, His angels, His Books, His Messengers, the Last Day, and to believe in al-qadar (the divine will and decree), both good and bad.” (Muslim)

Abu Bakr al-Isma‘ili said, “You should understand – may Allah have mercy on us and you – that the view of Ahl al-Hadith, Ahl al-Sunnah wa’l-Jama‘ah, is that we believe in Allah, His angels, His Books and His Messengers, and we accept what the book of Allah, may He be glorified and exalted, says and what is soundly narrated from the Messenger of Allah (blessings and peace of Allah be upon him).”

Scholarly consensus (ijma‘):
i. Ibn al-‘Attar said, “It is obligatory to believe in all the messengers and prophets of Allah, and to believe that everything they brought is true.… The scholars said: A man cannot be a believer unless he believes in all the previous prophets and all the books that Allah, may He be glorified and exalted, sent down to all the messengers… One who acknowledges that Allah is one and is the only one Who is deserving of worship, but denies prophethood completely, or denies the prophethood of our Prophet in particular, or denies the prophethood of one of the prophets mentioned in the religious texts after coming to know of that, is undoubtedly a disbeliever.”

ii. Ibn Taymiyah said, “The Muslims are unanimously agreed that what is well known and well established in Islam, and no one can claim not to know it, is that it is obligatory to believe in all the prophets and messengers, and in all the books that Allah sent down. Whoever disbelieves in even one prophet who is known to be a prophet – such as Ibrahim, Lut, Musa, Dawud, Sulayman, Yunus or ‘Isa – is a disbeliever according to all Muslims, and he comes under the same rulings as the disbelievers.”

Rational evidence for the obligation to believe in the messengers:

ii. The fact that Allah, may He be glorified and exalted, created people to worship Him dictates that He should choose messengers and send them to teach people how to worship and obey Him Allah, may He be glorified and exalted.
iii. The fact that reward and punishment are connected to the impact that obedience and disobedience have on the soul in terms of purifying it or otherwise is something which dictates that messengers and prophets should be sent so that people cannot say on the Day of Resurrection: O Lord, we did not know what obedience to You is so that we could obey You, and we did not know what disobedience to You is so that we could avoid it.

2.2. What is meant by believing in the prophets and messengers
Believing in the prophets and messengers (peace be upon them) includes several things:
i. Believing in those whom Allah, may He be glorified and exalted, has mentioned in His Book or mention of them were soundly narrated from His Messenger (blessings and peace of Allah be upon him).
ii. Believing that Allah, may He be glorified and exalted, has messengers and prophets other than those whose names He mentioned in His Book.
iii. Believing what they told us and believing that they conveyed everything with which they were sent.
iv. Regarding all of them as allies and loving them is obligatory, and hating them and regarding them as enemies constitutes disbelief.
v. Showing them due respect, without exaggerating about them or disrespecting them.
vi. Believing that Muhammad (blessings and peace of Allah be upon him) is the last of the prophets and that his message is for all the worlds, and that it is obligatory to believe him and follow the system of law that he brought, both in general terms and in specific terms.

2.2.1. Believing in those whom Allah, may He be glorified and exalted, has mentioned in His Book or mention of them were soundly narrated from His Messenger (blessings and peace of Allah be upon him)

Allah, may He be glorified and exalted, says (interpretation of the meaning), "And We have already sent messengers before you. Among them are those whose stories We have related to you, and among them are those whose stories We have not related to you." (Ghafir 40:78) 

Ibn Kathir said, “That is, We have revealed to you knowledge of some of them and their stories with their people, and how their people rejected them, then the Messengers ultimately prevailed and had a good outcome. and among them are those whose stories We have not related to you and they are many times more in number.” 

Ibn Abi’l-‘Izz said, “As for the prophets and messengers, we must believe in those of His Messengers whom Allah, may He be glorified and exalted, has mentioned by name in His Book, and we must believe that Allah, may He be glorified and exalted, sent messengers and prophets other than them, whose names and number no one knows except Allah, may He be glorified and exalted, Who sent them. We must believe in them in general terms, because there is no text which speaks of their number.” This implies that we must believe in all the messengers of Allah.

Allah, may He be glorified and exalted, says (interpretation of the meaning), "The Messenger has believed in what was revealed to him from his Lord, and so have the believers. All of them have believed in Allah and His angels and His books and His messengers, saying, “We make no distinction between any of His messengers.” And they say, “We hear and we obey. We seek Your forgiveness, our Lord, and to You is the final destination.” (al-Baqarah 2:285)

Al-Qurtubi said, “That is, they said: We believe in all the messengers and we do not disbelieve in any one of them; and we do not differentiate between them as the Jews and the Christians did.” So whoever disbelieves in one of them has disbelieved in Allah, may He be glorified and exalted, and in all His Messengers (peace be upon them). Allah, may He be glorified and exalted, says (interpretation of the meaning), "The people of Nuh rejected the Messengers." (al-Shu‘ara’ 26:105) "‘Aad rejected the Messengers." (al-Shu‘ara’ 26:123) "Thamud rejected the Messengers." (al-Shu‘ara’ 26:141) "The people of Lut rejected the Messengers." (al-Shu‘ara’ 26:160)

Ibn Taymiyah said, “One messenger came to each of these peoples, but they disbelieved in the entire concept of messengers, so they did not disbelieve in only one of them.” Allah, may He be glorified and exalted, says (interpretation of the meaning), "Those who disbelieve in Allah and His Messengers, and want to make a distinction between belief in Allah and belief in His Messengers, and say: We believe in some and disbelieve in others, and seek to adopt a way in between, it is they who are indeed disbelievers, and We have prepared for the disbelievers a humiliating punishment. To those who believe in Allah and His Messengers, and make no distinction between belief in any of them, He will give their due rewards. For Allah is Oft-Forgiving, Most Merciful." (al-Nisa’ 4:150-152)

Al-Bayhaqi said, “This verse indicates that Allah, may He be glorified and exalted, regards disbelief in one of His Messengers as being the same as disbelief in all of them, and He regards disbelief in all of them as disbelief in Him, as He says after that (interpretation of the meaning), 'To those who believe in Allah and His Messengers …' (al-Nisa’ 4:152) Thus it is proven that the good end is only for those who do not differentiate between the messengers of Allah, may He be glorified and exalted, and believe in all of them.”

Ibn Taymiyah said, “Belief in the Messengers should include all of them, loving them and not differentiating between them or discriminating between them; it means believing in all the messengers and in everything that was sent down to them.” 

Ibn Abi’l-‘Izz said regarding belief in the Messengers, “Whoever believes in some of them and disbelieves in some of them in fact disbelieves in all of them… because the reason for believing in some of them also exists in the one in whom he does not believe.”

2.2.3. Believing what they told us and believing that they conveyed everything with which they were sent
Allah, may He be glorified and exalted, says (interpretation of the meaning), "Indeed, We sent to every nation a Messenger saying: Worship Allah alone and shun false gods." (al-Nahl 16:36)

Ibn Taymiyah said, “The Prophet (blessings and peace of Allah be upon him) is the truthful and trustworthy one who explained to the people what was sent down to them of revelation; he is the one who conveyed the message of his Lord, addressing them in a clear Arabic tongue. Allah, may He be glorified and exalted, says (interpretation of the meaning), "We did not send any Messenger but he spoke in the language of his own people, in order to make things clear to them." (Ibrahim 14:4) … And Allah, may He be glorified and exalted, says (interpretation of the meaning), "Is the duty of the Messengers anything other than conveying the message in the clearest way?" (al-Nahl 16:35) …. These and similar verses indicate that the messengers had to convey the message in a clear way… And it is known that the messengers did what was required of them. Whoever suggests that the prophets lied or concealed anything yet still says that they are prophets is one of the worst and most evil type of hypocrites.” 

Ibn Daqiq al-Eid said, “Belief in the messengers of Allah means believing that they told the truth in what they told us about Allah, may He be glorified and exalted, that He supported them with miracles that confirmed their truthfulness; that they conveyed the messages from Allah, explaining to the accountable what Allah enjoined upon them; and that we must respect them and not differentiate between any of them.” 

Ibn Rajab said, “Believing in the Messengers requires us to believe in everything that they told us about the angels, the prophets, the books, the resurrection, the divine decree and other details that they have told us about the attributes of Allah and the description of the Last Day.” ‘Ali al-Qari said, “We are enjoined to believe in them and believe what they told us.”

2.2.4. Regarding all of them as allies and loving them is obligatory, and hating them and regarding them as enemies constitutes disbelief
Allah, may He be glorified and exalted, says (interpretation of the meaning), "And whoever is an ally of Allah and His Messenger and those who have believed - indeed, the party of Allah - they will be the triumphant." (al-Ma’idah 5:56)

Ibn Taymiyah said regarding this and similar verses, “Allah has enjoined taking them as allies, and taking them as allies dictates agreeing with them and following them, just as taking someone as an enemy dictates opposing them and keeping away from them.” Allah has warned against taking His Messengers as enemies, and He mentions that after mentioning taking Allah and His angels as enemies, and He stated that the punishment is the same for both. Allah, may He be glorified and exalted, says (interpretation of the meaning), "Whoever is an enemy to Allah and His angels and His messengers and Jibril and Mika’il - then indeed, Allah is an enemy to the disbelievers." (al-Baqarah 2:98)

Ibn Kathir said, “Allah, may He be glorified and exalted, says (interpretation of the meaning), 'Whoever takes Me and My angels and My messengers – and His Messengers include His Messengers both angelic and human – … then indeed, Allah is an enemy to the disbelievers. Instead of using the pronoun, He mentioned His name here, as He did not say, ‘then indeed He is an enemy to the disbelievers.’ (Al-Baqarah: 98) Rather He mentioned His name here to emphasize the meaning and make it clear, and to tell them that whoever takes the close friends of Allah as enemies has taken Allah as an enemy.” It was narrated that Anas (may Allah be pleased with him) said, "The Prophet (blessings and peace of Allah be upon him) said, 'No one of you truly believes until I am more beloved to him than his parents, his children and all people.'"Al-Sa‘di said regarding the Messengers, “It is obligatory to believe in them and in everything that they brought from Allah, and to love them and venerate them.”

2.2.5. Showing them due respect, without exaggerating about them or disrespecting them
Allah, may He be glorified and exalted, says (interpretation of the meaning), "O People of the Scripture, do not commit excess in your religion or say anything about Allah except the truth." (al-Nisa’ 4:171) 

Ibn Qasim said, “That is, do not go beyond the limit that Allah sets for you, and do not raise any created being above his appropriate status that Allah decreed for him. The People of the Book mentioned here are the Jews and Christians. Exaggeration is common among the Christians, for they exaggerated about ‘Isa, elevating him above the level of prophethood to the extent that they took him as a god besides Allah, whereas the Jews belittled him and regarded him as being beneath his appropriate status to the extent that they regarded him as illegitimate. Thus the Christians went to extremes in exaggerating about him and the Jews went to extremes in demeaning him.”

‘Umar ibn al-Khattab (may Allah be pleased with him) narrated that the Messenger of Allah (blessings and peace of Allah be upon him) said, “Do not exaggerate in praising me as the Christians exaggerated in praising the son of Maryam; I am only His slave, so say: The slave of Allah and His Messenger.” 

Ibn ‘Uthaymin said, “The words ‘I am only His slave’ mean: I have no right to claim lordship or any attribute that belongs solely to Allah, may He be glorified and exalted, ‘so say: The slave of Allah and His Messenger.’ These two attributes are the best and noblest attributes of the Messenger (blessings and peace of Allah be upon him), for Muhammad (blessings and peace of Allah be upon him) is a slave of Allah and cannot be worshipped, and he is a messenger and cannot be disbelieved.”

2.2.6. Belief in Muhammad (blessings and peace of Allah be upon him)
That includes believing that he is the last of the prophets and that his message is for all the worlds. Allah, may He be glorified and exalted, says (interpretation of the meaning), "And We have not sent you except comprehensively to mankind as a bringer of good tidings and a warner." 
(Saba’ 34:28) "Say, O Muhammad, “O mankind, indeed I am the Messenger of Allah to you all.” (al-A‘raf 7:158) "Muhammad is not the father of any one of your men, but he is the Messenger of Allah and last of the prophets." (al-Ahzab 33:40)

Al-Tahhawi said, “Muhammad is His chosen slave, His favored Prophet, His Messenger with whom He is pleased, and he is the last of the prophets, the imam of the pious, the leader of the messengers, the beloved of the Lord of the Worlds. Any claim of prophethood after him is misguidance and is based on whims and desires. He is the one who was sent to all of the jinn and all of humankind, with truth and guidance, light and illumination.”

Ibn Abi Ya‘la said, “Belief in Muhammad (blessings and peace of Allah be upon him) means believing that our Prophet Muhammad (blessings and peace of Allah be upon him) is the last of the prophets, the leader of the messengers, the imam of the pious and the messenger of the Lord of the worlds, whom He sent to us and to all of creation.”

Ibn Qudamah said, “If someone affirms that Muhammad is the Messenger of Allah (blessings and peace of Allah be upon him) but denies that he was sent to all the worlds (jinn and humankind), his faith cannot be valid unless he bears witness that Muhammad is the Messenger of Allah to all of creation.”

Abu’l-‘Abbas al-Qurtubi said, “Every Christian who hears of our Prophet and the teachings of Islam, then does not believe in him, his Christianity will not benefit him, because he failed to adhere to the covenant that was taken from him according to the teachings of his own religion.”

Believing in Muhammad (blessings and peace of Allah be upon him) means believing what he said and following the system of law that he brought, both in general terms and in specific terms. Muhammad ibn Nasr al-Marwazi said in his commentary on the hadith of Jibril (peace be upon him) about the pillars of faith: “…and to believe in Muhammad (blessings and peace of Allah be upon him); your belief in him is not like your belief in the other messengers, for your belief in the other messengers is acknowledging them, whereas your belief in Muhammad (blessings and peace of Allah be upon him) is acknowledging him, believing him, and following what he brought.”

Ibn Taymiyah said, “One of the things that you should know is that Allah sent Muhammad (blessings and peace of Allah be upon him) to all of humankind and the jinn, so there is no human or jinni but he must believe in Muhammad (blessings and peace of Allah be upon him) and follow him, and he must believe what he told us and obey what he enjoined on us. … Muhammad (blessings and peace of Allah be upon him) was sent to the two races of humankind and the jinn according to the consensus of the Muslims.”

Ibn Abi’l-‘Izz said, “With regard to believing in Muhammad (blessings and peace of Allah be upon him), it means believing him and following what he brought of laws and teachings, in general terms and in specific terms.”

Hafiz al-Hakami said, discussing the meaning of the testimony that Muhammad is the Messenger of Allah (blessings and peace of Allah be upon him), “It means believing firmly and wholeheartedly, and affirming verbally, that Muhammad is His slave and His Messenger to all humankind… So it is obligatory to believe everything that he told us about what came before and what is to come; to believe that what he permitted is permissible and what he prohibited is prohibited; to comply and submit to what he enjoined, and to give up and refrain from what he forbade; and to follow his teachings and adhere to his Sunnah.”

2.3. The benefits of believing in the prophets and messengers
The benefits of believing in the prophets and messengers (peace be upon them) include the following:
i. Strong faith in Allah, may He be glorified and exalted, and knowing His laws and guidance and how to implement them.
ii. Knowledge of Allah’s mercy and care for His creation, as He sent those noble Messengers to them to guide them and show them the right path.
iii. Affirmation of Allah’s wisdom in sending the Messengers.
iv. Gratitude to Allah, may He be glorified and exalted, for this immense blessing.
v. Love and respect for the Messengers, and praising them as they deserve.