The Prophet ﷺ said, "When the Imam says 'Amin', then you should all say 'Amin', for the angels say 'Amin' at that time, and he whose 'Amin' coincides with the 'Amin' of the angels, all his past sins will be forgiven." (Using translation from Bukhārī 6402)  

قَالَ رَسُولُ اللهِ ﷺ «إِذَا أَمَّنَ الْقَارِئُ فَأَمِّنُوا فَإِنَّ الْمَلَائِكَةَ تُؤَمِّنُ فَمَنْ وَافَقَ تَأْمِينُهُ تَأْمِينَ الْمَلَائِكَةِ غُفِرَ لَهُ مَا تَقَدَّمَ مِنْ ذَنْبِهِ»  

The Prophet ﷺ said, "When the Imam says 'Amin', then you should all say 'Amin', for the angels say 'Amin' at that time, and he whose 'Amin' coincides with the 'Amin' of the angels, all his past sins will be forgiven." (Using translation from Bukhārī 6402)  

عنِ النَّبِيِّ ﷺ قَالَ «إِذَا أَمَّنَ الْقَارِئُ فَأَمِّنُوا فَإِنَّ الْمَلَائِكَةَ تُؤَمِّنُ فَمَنْ وَافَقَ تَأْمِينُهُ تَأْمِينَ الْمَلَائِكَةِ غُفِرَ لَهُ مَا تَقَدَّمَ مِنْ ذَنْبِهِ»  

"The Messenger of Allah ﷺ said: 'When the Imam says: Not (the way) of those who earned Your anger, nor of those who went astray, say: 'Amin' for the angels say Amin and the Imam says Amin, and if a person's Amin coincides with the Amin of the angels, his previous sins will be forgiven.'" (Using translation from Nasāʾī 927)  

قَالَ رَسُولُ اللهِ ﷺ إِذَا قَالَ الْإِمَامُ {غَيْرِ الْمَغْضُوبِ عَلَيْهِمْ وَلَا الضَّالِّينَ} [الفاتحة 7] فَقُولُوا آمِينَ فَإِنَّ الْمَلَائِكَةَ تَقُولُ آمِينَ وَإِنَّ الْإِمَامَ يَقُولُ آمِينَ فَمَنْ وَافَقَ تَأْمِينُهُ تَأْمِينَ الْمَلَائِكَةِ غُفِرَ لَهُ مَا تَقَدَّمَ مِنْ ذَنْبِهِ  

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 الْإِمَامُ فَأَمِّنُوا فَإِنَّهُ مَنْ وَافَقَ تَأْمِينُهُ تَأْمِينَ الْمَلَائِكَةِ غُفِرَ لَهُ مَا تَقَدَّمَ مِنْ ذَنْبِهِ»