(112) باب فَضْلِ التَّأْمِينِ
Narrated Abu Huraira:
Allah's Messenger (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."
Reference: Sahih al-Bukhari 781
In-book reference: Book 10, Hadith 176
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 1, Book 12, Hadith 748