Abu Hurairah reported the Messenger of Allah (May peace be upon him) as saying; When the Imam says Amin, say Amin, for if anyone’s utterance of Amin synchronnises with that of the angles, he will be forgiven his past sins.Ibn shihab (al Zuhrl) said; The Messenger of Allah (May peace be upon him) used to say Amin (At the end of the Fatihah)