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 if a person's Amin coincides with the Amin of the angels, his previous sins will be forgiven.'" (Using translation from Nasāʾī 929)
أَنَّ رَسُولَ اللهِ ﷺ قَالَ إِذَا قَالَ الْإِمَامُ {غَيْرِ الْمَغْضُوبِ عَلَيْهِمْ وَلَا الضَّالِّينَ} [الفاتحة 7] فَقُولُوا آمِينَ فَإِنَّهُ مَنْ وَافَقَ قَوْلُهُ قَوْلَ الْمَلَائِكَةِ غُفِرَ لَهُ مَا تَقَدَّمَ مِنْ ذَنْبِهِ