Messenger of Allah ﷺ said, "If any one of you says, "Amin" and the angels in the heavens say "Amin" and the former coincides with the latter, all his past sins will be forgiven."  

أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ إِذَا قَالَ أَحَدُكُمْ آمِينَ وَقَالَتِ الْمَلاَئِكَةُ فِي السَّمَاءِ آمِينَ فَوَافَقَتْ إِحْدَاهُمَا الأُخْرَى غُفِرَ لَهُ مَا تَقَدَّمَ مِنْ ذَنْبِهِ