Waki' narrates likewise from Hammam that the Messenger of Allah (peace and blessings be upon him) said: "When you place your dead in their graves, say: 'Bismillah wa 'ala sunnati Rasulillah' (In the name of Allah and upon the Sunnah of the Messenger of Allah (peace and blessings be upon him))."
Only Hammam bin Yahya narrated it as marfu' (attributed to the Prophet) with this chain, and he is thiqah (trustworthy); however, Shu'bah and Hisham al-Dastuwa'i narrated it from Qatadah as mawquf (stopping) on Ibn Umar.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنائز / 7059