Musnad Ahmad 26:808

Abu Mu'awiyah narrated to us, Al-A'mash narrated to us, from Ibrahim, from Abd al-Rahman ibn Yazid, who said: "Abdullah threw seven pebbles at Jamrat al-Aqabah from the bottom of the valley, saying 'Allahu Akbar' with every pebble." It was said to him: "Indeed, some people throw them from above it." 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."