Sunan Ibn Majah: Book 0, Hadith 63

It was narrated that ‘Umar said: “We were sitting with the Prophet (ﷺ) when a man came to him whose clothes were intensely white and whose hair was intensely black; no signs of travel could be seen upon him, and none of us recognized him. He sat down facing the Prophet (ﷺ), with his knees touching his, and he put his hands on his thighs, and said: ‘O Muhammad, what is Islam?’ He said: ‘To testify that none has the right to be worshipped but Allah, and that I am the Messenger of Allah, to establish regular prayer, to pay Zakat, to fast in Ramadan, and to perform Hajj to the House (the Ka’bah).’ He said: ‘You have spoken the truth.’ We were amazed by him: He asked a question, then told him that he had spoken the truth. Then he said: ‘O Muhammad, what is Iman faith? He said: ‘To believe in Allah, His angels, His Messengers, His books, the Last day, and the Divine Decree (Qadar), both the good of it and the bad of it.’ He said’ You have spoken the truth.’ We were amazed by him. He asked a question, then told him that he had spoken the truth. Then he said: ‘O Muhammad, what is Ihsan (right action, goodness, sincerity)? He said: ‘To worship Allah as if you see Him, for even though you do not see Him, He sees you.’ He asked: “When will the Hour be?’ He said: ‘The one who is being asked about it does not know more than the one who is asking.’ He asked: ‘Then what are its signs?’ he said: ‘When the slave woman gives birth to her mistress’ (Waki’ said: This means when non-Arabs will give birth to Arabs”) ‘and when you see barefoot, naked, destitute shepherds competing in constructing tall buildings.’ The Prophet (ﷺ) met me three days later and asked me: ‘Do you know who that man was? I said” ‘Allah and his Messenger know best.’ He said: ‘That was Jibril, who came to you to teach you your religion.'”