Musnad Ahmad 22:30

Rawh narrated to us, Ibn Jurayj narrated to us, and Ibn Bakr said: Ibn Jurayj narrated to us, Abu al-Zubayr informed me that Abu Ma'bad, the freed slave of Ibn Abbas, informed him, from Abdullah ibn Abbas, from al-Fadl ibn Abbas, from the Messenger of Allah (peace and blessings of Allah be upon him), that he said on the evening of Arafah and the morning of Jam' (Muzdalifah) to the people when they departed: "Maintain tranquility." And he was restraining his she-camel until, when he entered Mina and descended into Muhassir, he said: "You must use the pebbles of al-khadhf (small pebbles) with which the Jamrah is pelted." And the Prophet (peace and blessings of Allah be upon him) was gesturing with his hand just as a person throws [pebbles].