Musannaf Ibn Abi Shayba 3:2358

Abu Bakr narrated to us, he said: Hushaym narrated to us, from Ayyub, from Abu al-Ala’, he said: Qatadah narrated to us, from Anas, he said: The Messenger of Allah (may Allah bless him and grant him peace) said: "Whoever forgets a prayer or sleeps through it, then his expiation is that he prays it when he remembers it."