Sayyiduna Ibn Umar (may Allah be pleased with them both) says that when the Prophet (peace and blessings be upon him) placed the deceased in the grave, he would say: "Bismillah, wa 'ala sunnati Rasulillah" (In the name of Allah, and upon the Sunnah of the Messenger of Allah).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنائز / 7058