The Book of Prayers (Kitab Al-Salat)

Muslim :: Book 4 : Hadith 811

Abu Huraira reported: The Messenger of Allah (may peace be upon him) said: SayAmin when the Imam says Amin, for it anyone's utterance of Amin synchronises with that of the angels, he will be forgiven his past sins.

Source materials are from the University of Southern California MSA site
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