Based on what do we believe in the existence of angels?
All of the heavenly religions, primarily Islam, informed us about the existence of angels; prophets saw them in their real forms and received revelation from them. The Quran and the other holy books mention the existence of angels. They give definite proof like seeing with eyes that angels exist.
It is great ignorance and denial not to believe in the existence of angels because one cannot see them with his eyes though the Quran and prophets agree unanimously on the existence of them. It is out of question for a person who believes in Allah not to believe in the existence of angels.
• Angels appeared to men in disguise in various forms with the order and permission of Allah. Gabriel (Jibril) appeared to the Prophet in the form of Dihya (one of the Companions); sometimes, he appeared as a stranger that nobody knew. (Bukhari, Iman 37; Muslim, Iman 1; Abu Dawud, Sunnah 15) It is stated in the Quran that Gabriel appeared to Maryam (Mary) in the form of a human being. (Maryam 19/16-17) It is also stated in the Quran that a group of angels went to Hazrat Ibrahim (Abraham) to give him the good news of having a son and inform him about the destruction of the tribe of Lot. (Hud, 11/69-70). That verse shows that angels do not eat or drink like human beings.