Musnad Ahmad 26:482

Ibn Numayr narrated to us, from al-A‘mash, from Ibrahim, from ‘Alqamah, from ‘Abdullah, who said: The Messenger of Allah (ﷺ) led us in prayer, and he either added or omitted [something]. Ibrahim said: The forgetfulness of that came only from me. We said: "O Messenger of Allah, has something been introduced into the prayer?" He said: "And what is that?" We said: "You prayed such and such." He said: "I am only a human being; I forget just as you forget. So if one of you forgets, let him perform two prostrations." Then he turned and performed two prostrations.