Abu Dawud Book 4, Hadith Number 1762.
Chapter : Not known.
Narated By Arfah ibn al-Harith al-Kandi : I was present with the Apostle of Allah (PBUH) 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 (PBUH) 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.