Sayyiduna Ghurfah bin al-Harith (may Allah be pleased with him) related: I was present with the Messenger of Allah (peace and blessings be upon him) at the Farewell Hajj. The sacrificial camels were brought, and he (peace and blessings be upon him) said: "Call Abu al-Hasan to me." So Sayyiduna Ali (may Allah be pleased with him) was called, and he (peace and blessings be upon him) said to him: "Take hold of the lower part of the spear." And the Messenger of Allah (peace and blessings be upon him) took hold of the upper part, and we slaughtered the camels with it. When he (peace and blessings be upon him) had finished, he mounted the mule and seated Sayyiduna Ali (may Allah be pleased with him) behind him.
Hadith Referenceالمعجم الكبير للطبراني / باب الغين / 15746