Musannaf Ibn Abi Shayba 8:1379

Abu Bakr narrated to us, he said: Ibn Idris narrated to us, from Layth, from Mujahid, from Muhammad ibn Abd al-Rahman ibn Yazid, from his father, who said: I went with Abdullah [ibn Mas'ud], and he threw seven pebbles. He kept the valley to his side [i.e., he stood in the bottom of the valley]. When he finished, he said: "O Allah, make it an accepted Hajj and a forgiven sin." Then he said: "This is how I saw the one upon whom Surah al-Baqarah was revealed act."