اللَّهُمَّ اغْفِرْ لَهُ اللَّهُمَّ ثَبِّتْهُ
Allāhumma’ghfir lah Allāhumma thabbit’h.
O Allah, forgive him. O Allah, strengthen him.
The Prophet (ﷺ) used to stop after burying the dead and say to the people: "Ask Allah to forgive your brother and pray for him to be strengthened, for indeed he is now being questioned." Abu Dawud 3/315, and Al-Hakim 1/370 who graded it authentic and Ath-Thahabi agreed.