Musnad Ahmad 26:1

Hushaym narrated to us, Mughirah narrated to us, from Ibrahim, Abd al-Rahman ibn Yazid narrated to us, he said: I saw Ibn Mas'ud throw the Jamrah, the Jamrat al-Aqabah, from the bottom of the valley. Then he said: "This—by the One besides whom there is no god—is the station of the one upon whom Surah al-Baqarah was revealed."