Sahih Muslim Book 19, Hadith Number 4438.

Chapter : The battle of Khaibar.

It has been narrated (through another chain of transmitters) on the authority of the same narrator (i.e. Anas) who said: I was riding behind Abu Talha on the day of the Battle of Khaibar (and we were riding so close to the Holy Prophet that) my foot would touch his We encountered the people at sunrise when they had come out with their axes, spades and strings driving their cattle along. They shouted (in surprise): Muhammad has come along with his force ! The Messenger of Allah (may peace be upon him) said: Khaibar shall face destruction. Behold ! when we descend in the city-square of a people, it is a bad day for those who have been warned (but have not taken heed). Allah, the Glorious and Majestic, inflicted defeat upon them.