Musannaf Ibn Abi Shayba 3:1971

Hushaym narrated to us, [who said] Abu Bishr narrated to us, from Yusuf al-Makki, from Ubayd ibn Umayr, that he said: The *aza'im* (obligatory/firm) prostrations are: *Alif-Lam-Mim Tanzil* (Surah as-Sajdah), *Ha-Mim Tanzil* (Surah Fussilat), *al-A'raf*, and *Banu Isra'il* (Surah al-Isra).