Sunan Ibn Majah, Chapter: The Chapters on Tribulations

"The Messenger of Allah (saw) came out one day to the people, and a man came to him and said: 'O Messenger of Allah, when will the Hour be?' He said: 'The one who is asked about it does not know more than the one who is asking. But I will tell you of its portents. When the slave woman gives birth to her mistress, that is one of its portents. When the barefoot and naked become leaders of the people, that is one of its portents. When shepherds compete in constructing buildings, that is one of its portents. (The Hour) is one of five (things) which no one knows except Allah.' Then the Messenger of Allah (saw) recited the words: "Verily, Allah, with Him (alone) is the knowledge of the Hour, He sends down the rain, and knows that which is in the wombs. (to the end of the Verse)."[31:34]