At the time of lowering the deceased in the grave, one should recite the following dua:
بِسمِ اللهِ وَبِاللهِ وَعَلىَ مِلَّةِ رَسُولِ اللهِ
In the name of Allah Ta‘ala, with the assistance of Allah Ta‘ala and upon the way of Rasulullah (sallallahu ‘alaihi wasallam) (I am lowering the deceased in the grave)
عن ابن عمر أن النبي صلى الله عليه وسلم كان إذا أدخل الميت القبر قال: بسم الله وبالله وعلى ملة رسول الله (سنن الترمذي، الرقم: 1046)
Hazrat ibnu Umar (radhiyallahu ‘anhuma) reports that whenever Rasulullah (sallallahu ‘alaihi wasallam) would lower the deceased into the grave, he would recite the following dua:
بِسمِ اللهِ وَبِاللهِ وَعَلىَ مِلَّةِ رَسُولِ اللهِ