What is the Hadith of Gabriel?

The hadith of Gabriel (as) is as follows:
Umar Ibn Al-Khattab (ra) reports:
“One day when we were with Allah’s Messenger (pbuh), a man with very white clothing and very black hair came up to us. No mark of travel was visible on him, and none of us recognized him. Sitting down beside the Prophet (SAW), leaning his knees against his and placing his hands on his things, he said:
“Tell me, Muhammad, about Islam.” He replied: “Islam means that you should testify that there is no god but Allah and that Muhammad (pbuh) is Allah’s Messenger, that you should observe the prayer, pay the Zakat, fast during Ramadan, and make the pilgrimage to the House if you are able to go there.” He said: “You have spoken the truth.” We were surprised at his questioning him and then declaring that he spoke the truth.
He said: “Now tell me about Iman.” He replied: “It means that you should believe in Allah (pbuh), His angels, His books, His messengers, and the Last Day, and that you should believe in the decreeing both of good and evil.”
Remarking that he had spoken the truth, he then said: “Now tell me about Ihsan.” He replied: “It means that you should worship Allah (swt) as though you see Him, for He sees you though you do not see Him.”
He said: “Now tell me about the Hour.” He replied: “The one who is asked about it is no better informed than the one who is asking.” He said: “Then tell me about its signs.” He replied:
“That a maid-servant should beget her mistress, and that you should see barefooted, naked, poor men and shepherds exalting themselves in buildings.”
[Umar] said: He then went away, and after I had waited for a long time, [the Prophet] said to me: “Do you know who the questioner was, Umar?” I replied: “Allah and His Messenger know best.”
He said: “He was Gabriel who came to you to teach you your religion.”
(Narrated by Bukhari)