We believe in angels and know with certainty that belief in them is the second among the pillars of faith. Allah Almighty says: {The Messenger believes in what has been sent down to him from his Lord, as do the believers. All of them believe in Allah, His angels, His Books, and His messengers.} [Surat al-Baqarah: 285] He, Exalted be He, also says: {It is not righteousness to turn your faces towards the east or the west, but righteousness is to believe in Allah, the Last Day, the angels, the Scriptures, and the prophets.} [Surat al-Baqarah: 177] Abu Hurayrah (may Allah be pleased with him) reported: The Messenger of Allah (may Allah's peace and blessings be upon him) came out to people one day, and someone came to him and said: "O Messenger of Allah, what is faith?" He replied: "To believe in Allah, His angels, His book, the meeting with Him, and His messengers, and believe in the Resurrection in the Afterlife." [Narrated by Al-Bukhāri (4777), Muslim (9), and Ibn Mājah (64)]
Al-Bayhaqi (may Allah have mercy upon him) said: "Belief in angels has various aspects, one of which is to believe in their existence, and another one is to give them their due status and affirm that they are servants of Allah and part of His creation like humankind and jinn; and they are subject to Allah's commands and accountable to Him; they have no power to do anything except what Allah enables them to; they can die, but Allah Almighty gave them a long term of life and will not cause them to die before they reach their appointed term; they should not be given any description leading to being associated as partners with Allah, Exalted be He, and should not be called upon as gods, as the earlier people used to do. (By the earlier people, they mean philosophers). The third aspect is to acknowledge that the angels include messengers whom Allah Almighty sends to whomever He wills from among humankind, and He may send them to one another. We should also acknowledge that they include the bearers of the Throne, angels who stand lined up in rows, gatekeepers for Paradise, gatekeepers for Hellfire, scribes who record people's deeds, and angels who direct the clouds. The Qur’an mentions all of this, or most of it." [Shu‘ab Al-Imān (1/296)]
So, Al-Bayhaqi mentioned three aspects of belief in angels.
The fourth aspect is to believe in angels both as a whole and individually. We believe in the existence of angels as a whole, and we also specifically believe in those angels whose names, traits, and actions are reported to us in the Qur’an or the Sunnah.
We are aware that what we do not know about their numbers, actions, and traits is more than what we know. However, we believe in all this, as we are informed by the Almighty Lord and His Messenger (may Allah's peace and blessings be upon him), without trying to know its very nature, rejecting it based on our limited minds, imagining it through our opinions, or interpreting it by our personal reasoning. Rather, we say: We believe and submit!