The Messenger of Allah ﷺ said: "When the Imam says Amin, say Amin, for if a person's Amin coincides with the Amin of the angels, his previous sins will be forgiven.'" (Using translation from Nasāʾī 928)
أَنَّ رَسُولَ اللهِ ﷺ قَالَ إِذَا أَمَّنَ الْقَارِئُ فَأَمِّنُوا فَإِنَّهُ مَنْ وَافَقَ تَأْمِينُهُ تَأْمِينَ الْمَلَائِكَةِ غُفِرَ لَهُ مَا تَقَدَّمَ مِنْ ذَنْبِهِ