Musannaf Ibn Abi Shaybah

It is narrated from Hazrat Umar that he said: We were sitting with the Prophet (peace and blessings be upon him) when a man came to him, dressed in very white clothes and with very black hair. There were no signs of travel visible on him, and none of us recognized him. He came close to the Prophet (peace and blessings be upon him) until he placed his knees close to the knees of the Prophet (peace and blessings be upon him) and placed his hands on his own thighs. He said, "O Muhammad (peace and blessings be upon him)! When will the Hour be established?" The Prophet (peace and blessings be upon him) replied, "The one being asked knows no more than the one asking. But among its signs are that a slave woman will give birth to her master, and that barefoot, naked, goat-herders will compete with one another in constructing tall buildings."