Also from ʿUmar (raḍiyallāhu anhu) who said:

"Whilst we were sitting with the Messenger of Allāh (ṣallallāhu ʿalayhi wasallam) one day, there came upon us a man whose clothes were intensely white and whose hair was intensely black. No sign of journey was visible on him and none of us knew him. He came and sat down by the Prophet (ṣallAllāhu ʿalayhi wasallam) (ṣallallāhu ʿalayhi wasallam), placing his knees by his (the Prophet's) knees and placed his hands on his thighs. He said, "O Muḥammad, inform me about Islām." The Messenger of Allāh said, "Islām is to bear witness that none has the right to be worshipped but Allāh and Muḥammad is the Messenger of Allāh, to establish the prayer, to pay the zakāh, to fast in Ramaḍān and to make pilgrimage to the House if you are able to do so." He (the man) said, "You have spoken truthfully," and we were amazed at his asking him and confirming he spoke truthfully. He said, "Then inform me about īmān." He said, "Īmān is to believe in Allāh, His Angels, His Books, His Messengers, the Last Day, and to believe in the Divine Decree (and foreknowledge)." He said, "You have spoken truthfully." He said, "Then tell me about īḥsān." He said, "It is to worship Allāh as if you can see Him, and even though you cannot see Him, He most certainly sees you." He said, "Then inform me of the Hour." He said, "The one being questioned about it is no more knowledgeable of it than the questioner." He said, "Then inform me of its signs." He said, "That the slave-girl will give birth to her own mistress and that you will see the barefooted, naked, destitute herdsmen competing in constucting lofty buildings." Then the man left and I stayed for a while. Then he (the Messenger) said, "O ʿUmar, do you know who the questioner was?" I said, "Allāh and His Messenger know best." He said, "That was Jibrīl, he came to teach you your religion."