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, ""When a slave (lady) starts giving birth to her master and when the shepherds of black camels start boasting and competing with others in the construction of tall buildings. And the Hour is one of five things which nobody knows except Allah."
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]