Musnad Ahmad 26:424

Yahya ibn Adam narrated to us, Abdullah ibn Idris narrated to us—he dictated it to me from his book—from Asim ibn Kulayb, from Abd al-Rahman ibn al-Aswad, Alqama narrated to us, from Abdullah, who said: "The Messenger of Allah (peace and blessings of Allah be upon him) taught us the prayer. He said 'Allahu Akbar' and raised his hands, then he bowed and joined his hands together, and placed them between his knees." This reached Sa'd, who said: "My brother has spoken the truth. We used to do that, then we were commanded to do this," and he took hold of his knees. Asim ibn Kulayb narrated it to me in this manner.