It was narrated from ‘Umar ibn al-Khattab (may Allah be pleased with him) that 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.” [5] Narrated by Muslim (8) in a lengthy hadith.

The one who denies the existence of the angels, takes them as enemies, reviles them or mocks them has disbelieved and rejected faith. Allah, may He be glorified and exalted, says, "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 Jarir said, “This is a statement from Allah, may He be glorified and exalted,… Informing us that whoever takes Jibril as an enemy has taken Him as an enemy, and he has taken Mika’il and all His angels and messengers as enemies, because those whom Allah names in this verse are close friends of Allah and those who obey Him; whoever takes as an enemy a close friend of Allah has taken Allah as an enemy and has declared war on Him.” [6] See: Tafsir Ibn Kathir, 2/301.

Comments of the scholars regarding that:
Ibn Hazm said, “The scholars are unanimously agreed that the angels are real, that Jibril and Mika’il are two angels and messengers of Allah, may He be glorified and exalted, who are close to Him and are of high status before Allah, may He be glorified and exalted, and that all the angels are believers.” [7] See: Maratib al-Ijma‘ (p. 174).
He also said, “It is soundly narrated that anyone who mocks Allah, may He be glorified and exalted, or one of the angels or one of the Prophets (peace be upon them), or a verse of the Qur’an or any of the obligatory duties of Islam – which are all signs of Allah, may He be glorified and exalted, – after proof has reached him is a disbeliever.” [8] See: al-Fasl, 3/142.
Ibn Taymiyah said, “Belief in the angels and jinn is something that is widespread among all the sons of Adam, and no one denies that except some odd people in some nations. Hence the disbelieving nations said: and if Allah had willed to send a messenger, He would have sent down angels al-Mu’minun 23:24.
Even the peoples of Nuh, ‘Ad, Thamud and Pharaoh said such things. The people of Nuh said, “This is not but a man like yourselves who wishes to take precedence over you; and if Allah had willed to send a messenger, He would have sent down angels.” (al-Mu’minun 23:24)
And Allah said, "But if they turn away, then say, “I have warned you of a thunderbolt like the thunderbolt that struck ‘Ad and Thamud.” (Fussilat 41:13)
“That occurred when the messengers had come to them before them and after them saying, “Worship not except Allah.” They said, “If our Lord had willed, He would have sent down the angels, so indeed we, in that with which you have been sent, are disbelievers.” (Fussilat 41:14)

Even though Pharaoh openly denied the Creator, the fact that he said, “Why have no armlets of gold been bestowed upon him, and why have no angels come with him to support him?” (al-Zukhruf 43:53) indicates that he must have heard of the angels, regardless of whether he acknowledged their existence or denied it. Awareness of the angels and the jinn is something that is common in all nations, and there is no nation that denies that completely. Rather only some of them deny that, such as those who delve into philosophy, who deny the existence of the angels because they have no proof that they exist, not because they have proof that they do not exist.” [9] See: al-Nubuwwat, 1/194.
Ibn Abi’l-‘Izz said, “The Qur’an is filled with mention of the angels, their types and their ranks… and the prophetic hadiths mention them a great deal. Hence belief in the angels is one of the five fundamentals or pillars of faith.” [10] See: Sharh al-Tahhawiyyah, 2/409.

2.2. What is meant by believing in the angels
Believing in the angels includes four things
i. Believing with certainty, beyond any shadow of a doubt, that they exist.
ii. Believing in what we know of their names (such as Jibril (peace be upon him)). As for those whose names we do not know, we believe in them in general terms.
iii. Believing in what we know of their physical attributes and character.
iv. Believing in what we know of their deeds. [11] See: Ibn ‘Uthaymin: al-Qawl al-Mufid, 2/410; Nubdhah min al-‘Aqidah, in Majmu‘ Fatawa Ibn ‘Uthaymin, 5/116; Salih al-Fawzan: al-Irshad ila Sahih al-I‘tiqad wa’l-Radd ‘ala Ahl al-Shirk wa’l-Ilhad, p. 167; ‘Abdullah al-Athari: al-Iman Haqiqatuhu Khawarimuhu Nawaqiduhu ‘inda Ahl al-Sunnah, p. 131.