Musannaf Ibn Abi Shaybah 4048 — Reports on one who forgets to recite

Jabir said: Amir (al-Sha'bi) and al-Hakam were asked about a man who forgets to recite Surah al-Fatihah in the prayer. Al-Sha'bi said: "He should perform the prostrations of forgetfulness (sajdah al-sahw)," and al-Hakam said: "He should recite Surah al-Fatihah when he remembers."