Musnad Ahmad 282:2

'Abd al-Razzaq narrated to us, he said: Ma'mar informed us, from Yazid ibn Abi Ziyad, from Sulayman ibn 'Amr ibn al-Ahwas, from his mother, and she had pledged allegiance to the Prophet, may God bless him and grant him peace. She said: I heard the Messenger of God saying while he was stoning the Jamrah from the bottom of the valley, and he was saying: "O people, do not kill one another. And when you stone the Jamrah, stone it with pebbles the size of those used for throwing (al-khadhf)."