Musannaf Ibn Abi Shayba 3:2456

Abu Bakr ibn Ayyash narrated to us, from al-A'mash, from Ibrahim, who said: If he intends to say "Sami' Allahu liman hamidah" (Allah hears those who praise Him), but says "Allahu Akbar" (Allah is the Greatest) instead, there is no forgetfulness (sahw) upon him.