Ibn 'Umar (RA) said, "The Messenger of Allah (ﷺ) used to say this dua when he put the dead body in the grave:

بِسْمِ اللَّهِ وَعَلَى سُنَّةِ رَسُوْلِ اللَّهِ (ﷺ)

Bismillaahi wa 'alaa sunnati Rasulillaah

With the Name of Allah and according to the Sunnah of the Messenger of Allah (ﷺ).

Reference: Sahih. Abu Dawud: 3213