Musnad Abu Ya'la al-Mawsili 162:15

Abu Bakr narrated to us, Abu Khalid narrated to us, from Ibn Jurayj, from Abu al-Zubayr, from Abu Ma'bad, from Ibn Abbas, from al-Fadl ibn Abbas, who said: The Messenger of Allah (peace and blessings of Allah be upon him) departed from Arafah and from Jam' (Muzdalifah) while he was composed, until he reached Mina. When he descended into [the valley of] Muhassir, he said: "O people, take [for yourselves] the pebbles of al-khadhf," meaning the pebbles for the stoning, gesturing with his hand [to indicate] the pebbles of al-khadhf.