The Prophet ﷺ said: "When the reciter says Amin, then say: "Amin" too, for the angels say Amin and if a person's Amin coincides with the Amin of the angels, Allah will forgive his previous sins" (Using translation from Nasāʾī 926)
النَّبِيَّ ﷺ إِذَا أَمَّنَ الْقَارِئُ فَأَمِّنُوا فَإِنَّ الْمَلَائِكَةَ تُؤَمِّنُ فَمَنْ وَافَقَ تَأْمِينُهُ تَأْمِينَ الْمَلَائِكَةِ غُفِرَ لَهُ مَا تَقَدَّمَ مِنْ ذَنْبِهِ