Musannaf Ibn Abi Shayba 3:2346

Abu Bakr narrated to us, he said: Hushaym narrated to us, he said: Yunus informed us, from al-Hasan and al-Mughirah, regarding the man who sleeps behind the Imam until the Imam bows and prostrates, then the sleeper wakes up. They both said: He follows the Imam and makes up what he missed of it.