`Umar ibn Khattab (Allah be well pleased with him) said:
“As we were sitting one day before the Messenger of Allah (peace and blessings be upon him), a man suddenly appeared. He wore pure white clothes and his hair was dark black—yet there were no signs of travel on him, and none of us knew him.
He came and sat down in front of the Prophet (peace and blessings be upon him), placing his knees against his, and his hands on his thighs. He said, “O Muhammad! Tell me about Islam.”
The Messenger of Allah (peace and blessings be upon him) replied, “Islam is to bear witness that there is no god but God and that Muhammad is the Messenger of God; and to perform the prayer; pay zakat; fast Ramadan; and to perform Hajj to the House if you are able.”
The man said, “You have spoken the truth,” and we were surprised that he asked and then confirmed the answer.
Then, he asked, “Tell me about belief (iman).”
The Prophet (peace and blessings be upon him) replied, “It is to believe in Allah; His Angels; His Books; His Messengers; the Last Day; and in destiny—its good and bad.”
The man said, “You have spoken the truth. Now, tell me about spiritual excellence (ihsan).”
The Prophet (peace and blessings be upon him) replied, “It is to serve Allah as though you behold Him; and if you don’t behold him, (know that) He surely sees you.”
“Now, tell me of the Last Hour,” asked the man.
The Prophet (peace and blessings be upon him) replied, “The one asked knows no more of it than the one asking.”
“Then tell me about its signs,” said the man.
The Prophet (peace and blessings be upon him) replied, “That slave women give birth to their mistresses; and that you see barefoot, unclothed, beginning shepherds competing in the construction of tall buildings.”
Then the visitor left, and I waited a long time. Then the Prophet (peace and blessings be upon him) asked me, “Do you know, Umar, who the questioner was?”
I replied, “Allah and His Messenger know best.”He said (Allah bless him and give him peace), “It was Jibril. He came to you to teach you your religion.” [Sahih Muslim]
