Abdullah bin al-Harith al-Azdi says: I heard Gharafah bin al-Harith al-Kindi (may Allah be pleased with him) say: I was present with the Messenger of Allah (peace and blessings be upon him) at the Farewell Hajj. The camels were brought, and he (peace and blessings be upon him) said: "Call Abu al-Hasan for me." So Sayyiduna Ali (may Allah be pleased with him) was called, and he (peace and blessings be upon him) said: "Take hold of the lower end of the spear." The Messenger of Allah (peace and blessings be upon him) took hold of its upper end. Then they both stabbed the camels with it. When he (peace and blessings be upon him) had finished, he mounted his mule and seated Sayyiduna Ali (may Allah be pleased with him) behind him.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 10220