Musnad Ahmad 26:392

Rawh narrated to us, Hammad narrated to us, from Hammad, from Ibrahim, from Abd al-Rahman ibn Yazid, that Abdullah ibn Mas’ud went into the interior of the valley and positioned himself across from the Jamarat, and he placed the mountain behind his back, then he threw [the pebbles]. And he said: "This is the station of the one upon whom Surat al-Baqarah was revealed."