Sunnan Abu Dawud Collection: ::Book Number 10:: Hadith # 1762
Narrated Arfah ibn al-Harith al-Kandi: I was present with the Apostle of Allah (peace_be_upon_him) at the Farewell Pilgrimage. When the sacrificial camels were brought to him, he said: Call AbulHasan (Ali) to me. Ali was then called for and he (the Prophet) said to him: Catch hold of the lower end of the lance, and the Apostle of Allah (peace_be_upon_him) himself caught hold of the upper end. He then pierced the camels with it. When he finished slaughtering, he rode on his mule and mounted Ali behind him.