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. (Using translation from Muslim 410f)
قَالَ رَسُولُ اللهِ ﷺ إِذَا قَالَ الْقَارِئُ {غَيْرِ الْمَغْضُوبِ عَلَيْهِمْ وَلَا الضَّالِّينَ} [الفاتحة 7] فَقَالَ مَنْ خَلْفَهُ آمِينَ فَوَافَقَ ذَلِكَ قَوْلَ أَهْلِ السَّمَاءِ آمِينَ غُفِرَ لَهُ مَا تَقَدَّمَ مِنْ ذَنْبِهِ