Sahih Muslim Book 19, Hadith Number 4318.

Chapter : Desirability of praying for victory at the time of confrontation with the enemy.

It is narrated on the authority of Anas that the Messenger of Allah (may peace be upon him) said on the day of the Battle of Ubud: O Allah, if Thou wilt (defeat Muslims), there will be none on the earth to worship Thee.