Sahih Muslim 1743
Sahih Muslim · Book 32: The Book of Jihad and Expeditions · It is recommended to pray for victory when meeting the enemy
It is narrated on the authority of Anas that the Messenger of Allah (ﷺ) said on the day of the Battle of Uhud:
وَحَدَّثَنِي حَجَّاجُ بْنُ الشَّاعِرِ ، حَدَّثَنَا عَبْدُ الصَّمَدِ ، حَدَّثَنَا حَمَّادٌ ، عَنْ ثَابِتٍ ، عَنْ أَنَسٍ ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم كَانَ يَقُولُ يَوْمَ أُحُدٍ " اللَّهُمَّ إِنَّكَ إِنْ تَشَأْ لاَ تُعْبَدْ فِي الأَرْضِ " .
O Allah, if Thou wilt (defeat Muslims), there will be none on the earth to worship Thee.