Narrated by Yazid Ibn Rukana Ibn Muttalib (RA): When the Messenger of Allah (ﷺ) perform Janazah prayer, he used to say:

اَللَّهُمَّ عَبْدُكَ وَابْنُ أَمَتِكَ اِحْتَاجَ إِلَى رَحْمَتِكَ، وَأَنْتَ غَنِيٌّ عَنْ عَذَابِهِ، إِنْ كَانَ مُحْسِنًا فَزِدْ فِي حَسَنَاتِهِ، وَإِنْ كَانَ مُسِيئًا فَتَجَاوَزْ عَنْهُ

Allaahumma 'abduka wabnu 'amatika ihtaaja 'ilaa rahmatika, wa 'Anta ghaniyyun 'an 'adhaabihi, 'in kaana mu'hsinan fazid fee hasanaatihi, wa 'in kaana musee'an fatajaawaz 'anhu

O Allah, he is the son of One of Your male & female slave, he is in need of Your mercy, and You are not in need of his torment. If he was pious, then increase his rewards and if he was a sinner then pardon him.

Reference: Sahih (Albani). Al-Hakim: 1/359