Abu Hurairah (RA) reported: The Messenger of Allah (ﷺ) said: When the Imam says: "Allah listens to him who praises Him." you should say: "O Allah, our Lord for Thee is the praise." for if what anyone says synchronises with what the angels say, his past sins will be forgiven.
Abu Hurairah (RA) reported: The Messenger of Allah (ﷺ) said: Say Amin 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.
Abu Hurairah (RA) reported: The Messenger of Allah (ﷺ) said: When anyone amongst you utters Amin in prayer and the angels in the sky also utter Amin, and this (utterance of the one) synchronises with (that of) the other, all his previous sins are pardoned.
Abu Harare reported: The Messenger of Allah (ﷺ) said: When anyone amongst you utters Amin and the angels In the heaven also utter Amin and (the Amin) of the one synchronises with (that of) the other, all his previous sins are pardoned.
'A hadith like this is transmitted by Ma'mar from Hammam bin Munabbih on the authority of Abu Hurairah (RA) who reported it from the Apostle of Allah (ﷺ) .
Abu Hurairah (RA) reported: The Messenger of Allah (ﷺ) said: When the reciter (Imam) utters: "Not of those on whom (is Thine) wrath and not the erring ones," and (the person) behind him utters Amin and his utterance synchronises with that of the dwellers of heavens, all his previous sins would be pardoned.