Reference : Hisn al-Muslim 126

اللّهُـمَّ إِنا نَجْـعَلُكَ في نُحـورِهِـم،
وَنَعـوذُ بِكَ مِنْ شُرورِهـمْ
Allāhumma innā naj`aluka fī nuḥūrihim 
wa na`ūdhu bika min shurūrihim.


O Allah, we ask You to restrain them by their necks,
and we seek refuge in You from their evil.

Reference:
Abu Dawud 2/89, and Al-Hakim graded it authentic and Ath-Thahabi agreed 
2/142.

Chapter: Upon encountering an enemy or those of authority