Musaddad said: Hammad bin Zayd narrated the hadith to us with the same chain and the same meaning, and added these words: It seems the Companions (may Allah be pleased with them) regarded the matter of that person as trivial, so he (peace and blessings be upon him) said: "Show me the grave." Then he (peace and blessings be upon him) came to the grave and offered the funeral prayer. Then he said: "These graves are filled with darkness for their occupants, and Allah Almighty illuminates them through my prayer."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنائز / 7013