Musnad Ahmad 33:1090

Rawh narrated to us, Ath-Thawri narrated to us, from Abu Az-Zubayr, from Jabir ibn Abdullah, who said: "The Messenger of Allah (peace and blessings of Allah be upon him) departed [from Arafat] while tranquility was upon him, and he commanded them to have tranquility, and he commanded them to throw [the pebbles] like the size of pebbles for throwing (al-khadhf). And he quickened his pace in the valley of Muhassir."