ḤADĪTH OF GABRIEL:

On the authority of Umar (r) who said: “One day while we were sitting with the Messenger of Allah (s), there came before us a man with extremely white clothing and extremely black hair. There were no signs of travel on him and none of us knew him. He [came and] sat next to the Prophet (s). He supported his knees up against the knees of the Prophet (s) and put his hand on his thighs.

He said, ‘O Muhammad, tell me about Islam.’ The Messenger of Allah (s) said, ‘Islam is to testify that there is none worthy of worship except Allah and that Muhammad is the Messenger of Allah, to establish the prayers, to pay the zakat, to fast [the month of] Ramadan, and to make pilgrimage to the House if you have the means to do so.’ He said, ‘You have spoken truthfully [or correctly].’ We were amazed that he asks the question and then says that he had spoken truthfully.
He said, ‘Tell me about ʾĪmān (faith).’ He [the Messenger of Allah (s)] responded, ‘It is to believe in Allah, His angels, His books, His messengers, the Last Day and to believe in the divine decree, [both] the good and the evil thereof.’ He said, ‘You have spoken truthfully.’ He said, ‘Tell me about al-Iḥsān (goodness).’ He [the Prophet (s)] answered, ‘It is that you worship Allah as if you see Him. And even though you do not see Him, [you know] He sees you.’
He said, ‘Tell me about [the time of] the Hour,’ He [the Prophet (s)] answered, ‘The one being asked does not know more than the one asking.’ He said, ‘Tell me about its signs.’ He answered, ‘The slave-girl shall give birth to her master, and you will see the barefooted, scantily-clothed, destitute shepherds competing in constructing lofty buildings.’
Then he went away. I stayed for a long time. Then he [the Prophet (s)] said, ‘O Umar, do you know who the questioner was?’ I said, ‘Allah and His Messenger know best.’ He said, ‘It was [the angel] Gabriel who came to teach you your religion.’” [Source: Saḥīḥ Muslim]