It is narrated from Sayyiduna Buraydah (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) offered the (funeral) prayer at a grave after the person had been buried.
Imam al-Tabarani (may Allah have mercy on him) said: "No one narrated this hadith from Alqamah bin Marthad except Abu Sinan, and Mihran is alone in narrating it; and this hadith is narrated from Buraydah (may Allah be pleased with him) only with this chain."
Hadith Referenceالمعجم الأوسط / باب الميم / 5554
Hadith Takhrij«أخرجه ابن ماجه فى «سننه» برقم: 1532، والبيهقي فى «السنن الكبرى» برقم: 7120»