Musnad Ahmad 27:222

Yahya narrated to us, from Ubaydullah, Nafi’ informed me, from Ibn Umar, who said: The Messenger of Allah (peace and blessings of Allah be upon him) used to recite the Surah to us, and he would recite the prostration (verse), so he would prostrate, and we would prostrate with him, until one of us would not find a place for the position of his forehead.