The first topic: Insulting the Messenger ?
Disbelief of and killing the one who insulted the Prophet ?
Among the characteristics of the Prophet ? is maintaining disbelief of and killing of those who insulted him. That is why when a man became harsh towards Aboo Bakr as-Siddeeq, Aboo Barzah said, “Shall I not strike his neck?” He rebuked him and said, “It (the injunction) is not for anyone after the Messenger of Allah ?.” [478]Narrated by an-Nasaa’ee (4071), and Ahmad (54), and the wording is his is from the hadeeth of Aboo Barzah (may Allah be pleased with him).  Classified as authentic by al-Albaanee in “Saheeh Sunan al-Nasaa’ee” (4071), and its chain of transmission was authenticated by Ahmad Shaakir in the takhreej of “Musnad Ahmad” (1/44), and Shuayb Al-Arnaa’oot in the takhreej of “Musnad Ahmed” (54).
On the authority of ‘Urwah ibn Muhammad, on the authority of a man from Balqain who said, “A man used to insult the Prophet ?. The Prophet ? said, “Who will suffice me from an enemy to me?” Khaalid ibn al-Walid replied, “I will.” So, the Prophet ? sent him and he killed him.” [479] Abd al-Razzaq (9705), and Ibn Hazm in Al-Muhalla, (11/413), and the wording is his, and it was authenticated.
Aboo Yoosuf says: “Any Muslim man who insults the Messenger of Allah ? or disaffirms him, or finds fault in him, or degrades him, then he has disbelieved in Allah, and his wife will be separated from him. If he repents, that is acceptable, or else he will be killed.” [480] Al-Kharaj, (p. 199).
Muhammad ibn Sahnoon says, “Scholars are unanimously agreed that the one who insults the Prophet ? and who belittles him is an infidel, and the threat is against him of Allah’s punishment for him, and his ruling according to the Ummah is death, and whoever doubts in his unbelief and his punishment has committed disbelief.” [481] Ash-Shifaa, by Iyad (2/215).
Ibn Hazm says, “Everyone who harms the Messenger of Allah ? is an apostate, an infidel and must be killed.” [482] Al-Muhalla, (11/414).

Evidence for the infidelity of the one who insults the Messenger ?
Section One: Evidence from the Quran of the infidelity of the one who insults the Messenger ?
1-   Allah, the Exalted, states, “And among them are those who abuse the Prophet and say, "He is an ear." Say, "It is an ear of goodness for you that believes in Allah and believes the believers and is a mercy to those who believe among you." And those who abuse the Messenger of Allah - for them is a painful punishment. They swear by Allah to you Muslims to satisfy you. But Allah and His Messenger are more worthy for them to satisfy, if they were to be believers. Do they not know that whoever opposes Allah and His Messenger - that for him is the fire of Hell, wherein he will abide eternally? That is the great disgrace.” At-Tawbah: 61-63
Ibn Taymiyyah says in his statement about these ayaat, “It is known that harming the Messenger of Allah is a hostility (opposition) against Allah and His Messenger because the mention of harming (abusing) is what necessitated the mention of hostility. It must be included in it, and if not for that, the speech would not have been harmonious, if it could be said: He is not hostile (opposer). This indicates that abusing and opposing are both acts of Kufr.” [483] Al-Saarim Al-Maslool, (2/58).
2-   Allah, the Glorified, states, “The hypocrites are apprehensive lest a surah be revealed about them, informing them of what is in their hearts. Say, ‘Mock as you wish; indeed, Allah will expose that which you fear.’ And if you ask them, they will surely say, ‘We were only conversing and playing.’ Say, ‘Is it Allah and His ayaat and His Messenger that you were mocking?’ Make no excuse; you have disbelieved i.e., rejected faith after your belief. If We pardon one faction of you - We will punish another faction because they were criminals.”  At-Tawbah
Ibn Taymiyyah says, “This is a textual evidence concerning the fact that mocking Allah, His signs, and His Messenger, is tantamount to Kufr; thus, the intended insult is by priority, worse, and this ayah indicates that anyone who belittles the Messenger of Allah ? seriously or jokingly has committed an act of disbelief.” [484] Al-Saarim Al-Maslool, (2/70).

Section 2:  Evidence from the Sunnah concerning killing the one who insults the Messenger ?
1-   On the authority of Jabir ibn Abdullah, may Allah be pleased with them both, he said: “The Messenger of Allah ? said, “Who is going to Ka’b ibn al-Ashraf? He has harmed Allah and His Messenger.” Muhammad ibn Maslamah got up and said, “O Messenger of Allah? Should I kill him?” He replied, “Yes... .” So, they killed him. Then they came to the Prophet ? and informed him of that.” [485] Narrated by Al-Bukhaaree (4037) and the wording is his, and Muslim (1801).
Aboo al-Abbaas al-Qurtubee says, “This man, Ka’b, was from Banu Nabhaan from the tribe of Taiyy, and his mother was from Banu an-Nadir, and he was a poet. The Prophet ? had made a covenant with him that the latter would not help against him, nor expose himself to harm him, nor to harm the Muslims, however he broke the covenant. He went to Makkah after the Battle of Badr, and he began to weep for the disbelievers who had been killed and incited them against the Messenger of Allah ?, and he was the one who tempted the Quraysh and others until they gathered for the Battle of Uhud. Then he returned to his lands and began to satirise the Messenger of ? and verbally harm him and the Muslims. At that moment, the Messenger of Allah ? said, “Who is going for Ka’b ibn al-Ashraf? He has indeed harmed Allah and His Messenger.” So, he tempted to kill him, and notified about the legal reason for that, and that he deserved to be killed.” [486] See al-Mufhim limaa Ashkala min Talkhees Kitaab Muslim, vol. 3, p. 659.
2-   On the authority of Aboo Barzah, he said: “A man acted harshly to Aboo Bakr as-Siddeeq.” I asked: “Should I kill him?” He rebuked me and said: “This (injunction) is not for anyone after the Messenger of Allah.” [487]. An-Nasaai (4071), it is his wording; and Ahmad (54).
Ibn Taymiyyah says, “Groups of scholars have inferred by this that it is permissible to kill a slanderer of the Prophet ?, these include Aboo Dawud, Ismail ibn Is-haaq al-Qadi, Aboo Bakr Abdul Aziz, al-Qadi Aboo Ya’la, and others among the scholars.” [488] As-Saarim al-Maslool, vol. 2, p. 193.
Insulting the Prophets
Ibn Hazm, “We have learned from the necessity of observation that every insulter and ridiculer do belittle the one they insulted and deride him. Belittling and mocking are the same thing, and we find that Allah Almighty made Satan, due to disregarding Adam, peace be upon him, an unbeliever because he said, “I am better than him,” Saad: 76, He, the Exalted, ordered him to leave paradise, and evicted him, and called him a disbeliever by saying, “And he was of the unbelievers.” Saad: 74.   …  So, it is correct with what we mentioned that everyone who insults Allah Almighty ... or insults a Prophet of the Prophets, or mocks him ... is thus an apostate infidel, who receives the judgement of an apostate, and this is what we say.” [489] See al-Muhalla, vol.11, p.412.
‘Iyaad says: “The ruling on one who insults all the prophets of Allah Almighty and His angels, and belittles them or disaffirms them in what they brought, or denies them and rejects them is exactly as the ruling concerning what one may do against our Prophet ?.” [490] See ash-Shifaa, vol.2, p.302.
Ibn Taymiyyah says, “One of the characteristics of the prophets is that whoever insulted a prophet will be killed by agreement of the imams, and he will be classed as an apostate, just as whoever disbelieved in him and what he brought is an apostate, for faith is only complete be believing in Allah, His angels, His Books, and His Messengers.” [491] As-Safadiyyah, (1/261).
He also said, “The Muslims believe in them i.e.: in the prophets, all of them, and did not differentiate between any of them, for belief in all the prophets is an imperative obligation, and whoever disbelieves in one of them then he disbelieves in all of them, and whoever insults a prophet among the prophets is an unbeliever whose killing is obligatory by agreement of the scholars.” [492] As-Safadiyyah, (2/311).
From the reports of the imams of the Mathhabs on that:
Ibn Nujaym al-Hanafee says, “He will be a disbeliever if he believes that Allah is pleased with disbelief, ... and due to not recognizing some of the prophets, peace be upon them, or due to finding a fault in a prophet flaw, or dissatisfaction with a way among the ways of the Messengers.” [493] Al-Bahr Al-Ra’iq, (5/129).
Al-Dardeer al-Maalikee says: “Whoever insults a prophet on whose prophecy there is a unanimous agreement, or insults a prophet, by saying when he is mentioned: ‘As for me, I am not a fornicator or a thief;’ then he has disbelieved. Similarly, if he attributes a shortcoming in a prophet, such as that he is bodily lame and paralysed; or about the knowledge that he possesses; for every prophet is the most knowledgeable of the people of his time, and their master Muhammad ? is the most knowledgeable of creation.” [494] Hashiyah Al-Saawee on Al-Sharh Al-Sagheer li Ad-Dardeer, (4/435).
Al-Sharbini Ash-Shaafi’ee says, “Whoever disaffirms a Messenger or a Prophet, or insults or belittles him or his name, ... then he has disbelieved.” [495] Mughnee Al-Muhtaaj, (5/429).
And Mar’i ibn Yoosuf al-Karmi al-Hanbalee says, “Whoever insults a Messenger ... then he has disbelieved.” [496] Ghayat Al-Muntaha, (2/498) briefly.