The Messenger of Allah ﷺ said: "If any one of you says: 'Amin' and the angels in Heaven say Amin, and the one coincides with the other, his previous sins will be forgiven." (Using translation from Nasāʾī 930)
أَنَّ رَسُولَ اللهِ ﷺ قَالَ إِذَا قَالَ أَحَدُكُمْآمِينَ قَالَتِ الْمَلَائِكَةُ فِي السَّمَاءِ آمِينَ فَوَافَقَتْ إِحْدَاهُمَا الْأُخْرَى غُفِرَ لَهُ مَا تَقَدَّمَ مِنْ ذَنْبِهِ