Musannaf Ibn Abi Shayba 21:731

Isma'il ibn 'Ulayyah narrated to us, from 'Ubayd Allah ibn Abi Bakr, who said: When Anas ibn Malik would level the grave over the deceased, he would stand over it and then say: "O Allah, Your servant has returned to You, so be gentle with him and have mercy on him. O Allah, distance the earth from his sides, open the gates of the heaven for his soul, and accept him from Yourself with a good acceptance. O Allah, if he was a doer of good, then multiply for him his good deeds, and if he was a doer of evil, then overlook his evil deeds."