Sahih Bukhari Volume 9, Book 88, Hadith Number 249.

Narrated By Zainab bint Jahsh : That one day Allah’s Apostle entered upon her in a state of fear and said, “None has the right to be worshipped but Allah! Woe to the Arabs from the Great evil that has approached (them). Today a hole has been opened in the dam of Gog and Magog like this.” The Prophet made a circle with his index finger and thumb. Zainab bint Jahsh added: I said, “O Alllah’s Apostle! Shall we be destroyed though there will be righteous people among us?” The Prophet said, “Yes, if the (number) of evil (persons) increased.”