Prophet (SAW)'s Prayers When fearing the enemy

Recite:

اللَّهُمَّ إِنَّا نَجْعَلُكَ فِي نُحُورِهِمْ وَنَعُوذُ بِكَ مِنْ شُرُورِهِمْ

"O Allah, we make you the turner of the (enemies) chest (heart) and seek refuge in You from their evils". (Abu Dawood)