Mishkat al-Masabih 825 — Prayer

Abu Huraira reported God’s Messenger as saying, “Say Amen when the imam says it, for if anyone’s utterance of Amen synchronises with that of the angels, he will be forgiven his past sins. ’ (Bukhari and Muslim.) In a version he said, “When the imam says, ‘Not of those with whom Thou art angry nor of those who go astray’, say Amen, for if anyone’s words synchronise with those of the angels he will be forgiven his past sins.” This is Bukhari’s wording, and Muslim has something similar. In another version by Bukhari he said, “Say Amen when the reciter (i.e. the imam) says it, for the angels do so, and if anyone’s utterance of Amen synchronises with that of the angels, he will be forgiven his past sins.”