Abd al-Rahman bin Abi Layla narrates from Sayyiduna Ali (may Allah be pleased with him) that when the Messenger of Allah (peace and blessings be upon him) slaughtered his camels, he (peace and blessings be upon him) slaughtered two-thirds of them with his own hand; then he (peace and blessings be upon him) ordered me, and I slaughtered all the rest.
Muhammad bin Ishaq bin Yasar narrated it thus, and the narration of Ja'far is more authentic. And Allah knows best.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 10224