Abu Hurairah narrated that :the Prophet said "When the Imam says 'Amin' then (all of you) say 'Amin.' For whoever's 'Amin' concurs with the 'Amin' of the angels, then his past sins will be forgiven"
SahihSahihHasan SahihBook 2 · Hadith 102
جامع الترمذي
Abu Hurairah narrated that :the Prophet said "When the Imam says 'Amin' then (all of you) say 'Amin.' For whoever's 'Amin' concurs with the 'Amin' of the angels, then his past sins will be forgiven"