Abu Dawud Book 4, Hadith Number 1917.

Narated By Ali ibn AbuTalib : The Prophet then took up Usamah behind him (on the camel), and drove the camel at a quick pace. The people were beating their camels right and left, but he did not pay attention to them; he was saying: O people, preserve a quiet demeanour. He proceeded (from Arafat) when the sun had set.