Mas'ud bin al-Hakam narrates from Ali bin Abi Talib (may Allah be pleased with him) that standing for the funeral (until it is set down) was mentioned before him, and Ali bin Abi Talib (may Allah be pleased with him) said: He (peace and blessings be upon him) stood up, then sat down. In another narration: He (peace and blessings be upon him) used to stand for funerals, then afterwards he sat.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنائز / 6884