Dua when deceased is an adult

Allahummaghfir li-hayyina wa mayyitinâ wa shâhidinâ wa ghâ’ibinâ wa saghirinâ wa kabirinâ wa dhakarinâ wa un-thânâ. Allâhumma man ah-yaytahu minnâ fa ah-yihi alal islâmi, waman tawaffaytahu minnâ fatawaffahu alal-iman.

O Allah, forgive our living and our deceased, our present and absent, our young and old, our men and women. 0 Allah, whomever You give life to, let him live on Islam and whomever You give death to, let him die on Imán. (Tirmidhi)

Note: The above-mentioned two duas  should be recited after the third takbir in salát al-janázah.