اَللَّهُمَّ اغْفِرْ لَهُ وَثَبِّتْهُ

Allahum-maghfir lahu wa thabbithu

O Allah, forgive him, strengthen him (During question of grave) Narrated Uthman ibn Affan (RA) : Whenever the Prophet (ﷺ) became free from burying the dead, he used to stay at him (i.e. his grave) and say: Seek forgiveness for your brother, and beg steadfastness for him, for he will be questioned now.

Reference: Sahih. Abu Dawud: 3221