اللَّهُمَّ اغْفِرْ لَهُ وَثَبِّتْهُ
Transliteration
Allahummaghfir lahu wa thabbit-hu
English meaning
O Allah, forgive him and make him steadfast.
When is it recited?
Recited at the graveside immediately after burial.
Its virtue
The Prophet (PBUH) used to stand at the graveside after burial and recite this.
Source
Abu Dawud, Jana'iz 73, 3221