Part of belief in the unseen is belief in the angels, peace be upon them, and belief in the jinn.
Belief in angels is a firm acknowledgment of their existence, and that they are of Allah Almighty’s creation, and that they are, “they1 are but honoured servants. They cannot precede Him in word, and they act by His command.” Al-Anbiyaa’: 26-27. And they are, “They do not disobey Allah in what He commands them but do what they are commanded.” At-Tahreem: 6. Further, it is obligatory to have faith in those who are mentioned in the Quran and the Sunnah in detail, just as it is obligatory to have faith in their physical and moral qualities, and the actions that they perform. Belief in angels is one of the pillars of faith, and the faith of a servant is not realized until he believes in them.
Ibn Abee al-‘Izz says, “Belief in angels is one of the five foundations which are the pillars of faith.” [513] Sharh at-Tahaawiyyah, (2/410).
It is also obligatory to believe in the existence of the jinn, and that they are a creation of Allah Almighty, and that they are alive, sane, and commanded and forbidden. [514] The Noble Qur’an and the Prophet’s Sunnah have extensively discussed the jinn and their conditions in many places; They are mentioned in the Qur’an in several places, close to forty, except for the ayaat that spoke about Satan, which are many. See: Al-Mu’jam al-Mufarhas li Alfaazh al-Qur’an, The Indexed Dictionary of the Words of the Qur’an, (p.: 179); ‘Aalam al-Jinn, The World of the Jinn, by Al-Ashqar (p.: 10)
And there are statements that contradict this belief, such as denying the existence of angels or the jinn or insulting and mocking the angels. The reason for the fact that these sayings contradict this belief are the following:
1-   Denying the existence of angels or jinn [515] Examples of this denial are: What atheist philosophers think is that angels are forces of a good soul, and demons are forces of an evil soul. See: Majmoo’ al-Fataawaa, by Ibn Taymiyyah (4/346). is a denial and rejection of the correct and explicit evidence from the Book and the Sunnah; the texts of the Noble Quran and the Prophet’s Sunnah have been abundantly frequent in talking about angels and jinn, and therefore the existence of angels and jinn is a Mutawaatir (widely and frequently narrated) and well-known matter of the religion of Islam. In the matter of the angels, peace be upon them, Allah Almighty said: “The Messenger believes in what was sent down to him from his Lord, and the believers too, each believe in God, His angels, His books, and His Messengers.”  Al-Baqarah: 286.
Allah, the Glorified, states, “And whoever disbelieves in Allah, His angels, His Books, His Messengers, and the Last Day, he has indeed gone far astray.”   An-Nisaa’’: 136 
As for the jinn, the Noble Quran, and the Prophetic Sunnah have extensively talked about the jinn and their conditions, and an entire surah is singled out in the hadeeth about a group of the jinn who listened to the Quran from the Messenger of God (may God bless him and grant him peace), just as it has been mentioned in detail in Surah al-Jinn.
Ibn Battah said, “Whoever denies the jinn is an infidel in Allah, a rejector of His ayaat, and denier of His Book.” [516] Al-Ibaanah Al-Sughra, (p.: 235).
Al-Qurtubee said, “A group of infidel physicians and philosophers have denied the jinn...by being presumptuous and slandering against Allah, and the Quran and the Sunnah refute them.” [517] See: Tafseer Al-Qurtubee, (19/6).
Denying the angels and the jinn is contrary to belief in the revealed books. Belief in the Books includes acknowledgment of and belief in them, and denial of the angels and jinn is a disaffirmation and rejection of the ayaat of Allah Almighty, as it contradicts this affirmation and belief.
2-   The scholars are unanimously agreed that whoever denies the angels or the jinn, or mocks and belittles the angels, or insults them is an infidel.
‘Iyaad said, “The ruling on one who insults all the prophets of Allah Almighty and His angels, and belittles them, or disaffirms them about what they brought, or denies them and rejects them is as the ruling concerning our Prophet ?  . [518] It is well known that insulting the Messenger, may Allah’s salutations and peace be upon him, or mocking him or denying him are among the nullifiers of faith by consensus. ” [519] Ash-Shifaa, (2/302).
If the scholars have unanimously agreed on the unbelief of the one who denies a ayah from the Book of God Almighty [520] See: Al-Ibaanah Al-Sughra, by Ibn Battah (p. 221), Al-Tamheed, by Ibn Abd Al-Bar (4/226), Ash-Shifaa, by Iyad (2/289). , then how can one who denies so many ayaat that prove the existence of angels and jinn?! The existence of angels, peace be upon them, and the jinn, as is proven in the Book and the Sunnah, is also unanimously established.
Ibn Hazm says, “They agreed that the angels are true, that Jibreel (Gabriel) and Mikaa’eel (Michael) are two angels who are messengers of Allah, the Mighty and Sublime, who are great and very close to Allah Almighty, and that the angels are all believers and virtuous, and that the jinn are true.” [521] Maraatib al-Ijmaa’, p.174.
Ibn Uthaymeen says, “The jinn are a reality, and their denial is a disaffirmation of the Quran, and a disbelief in Allah, the Mighty and Sublime.” [522] Fataawaa Noor ‘ala ad-Darb, (4/2).
3-   Belief in the angels, peace be upon them, necessitates venerating and honouring them, for they are honoured servants, who do not disobey Allah what He commands them, and do as they are commanded, and they glorify the night and day without ceasing; therefore, insulting and mocking them are not combined with their veneration and honour, even if the insult acknowledges their existence. This is due to the lack of appreciation of Allah Almighty, the way He needs to be appreciated and mockery of the ayaat of Allah Almighty.
Ibn Hazm says, “It is correct by textual evidence that everyone who mocks Allah Almighty, or an angel of the angels, or a prophet from among the prophets, peace be upon them, or a ayah from the Quran, or an obligation of the religion; all of them are the ayaat of Allah Almighty, after the deliverance of evidence to him, then he is a disbeliever.” [523] Al-Fasl, (3/142).
4-   Belief in the angels, peace be upon them, requires their love and affection. Allah, the Exalted, says, “Whoever is an enemy to Allah and His angels and His messengers and Gabriel and Michael - then indeed, Allah is an enemy to the disbelievers.” Al-Baqarah: 98
Al-Baydaawee says, “He, the Almighty, singled out the two angels by mentioning their merits as if they were of another kind and to warn that enmity with one and all is equal in disbelief and eliciting enmity from Allah Almighty, and that he who is hostile to one of them is as if he is hostile to them all, and because the motive of their enmity and love in reality is the same; this is because the controversy was about these two angels. The placement of the apparent noun (the disbelievers) in place of a pronoun is indicative that Allah harbours enmity against them due to their disbelief and that the enmity against the angels and messengers is an act of disbelief.” [524] Tafseer Al-Baydaawee, (1/96).
It has been established among scholars that denying the existence of the angels, peace be upon them, or insulting them or mocking them are among the nullifiers of faith.
Ibn Qudaamah said, “If he apostatises with denial of an obligation, he will not be safe until he confesses what he denied, and repeats the two testimonies because he disaffirmed in Allah and His Messenger with what he believed. Likewise, if he denies a prophet, or a ayah from the Book of Allah Almighty, or a Book from his Books, or an angel of his angels who are proven to be Allah’s angels, or he deemed a prohibited thing as permissible; in his Islam, he must affirm what he has denied.” [525] Al-Mughnee, (12/288).
An-Nawawee said, “If a person said: ‘If the prophets and angels testified about such things to me, I would not have believed them;’ then he has disbelieved.” [526] Rawdat Al-Taalibeen, (10/66).
Ad-Dardeer says, “He is an apostate if he insults a prophet on whose prophethood there is a unanimous agreement, or an angel on whose being an angel there is a unanimous agreement or exposes a prophet or an angel to an insult.” [527] Sharh Al-Saawee ‘ala Al-Sharh Al-Sagheer li Al-Dardeer,, (4/436).