Hadith #585 (Sunan Ibn Majah)
Book: Establishing the Prayer and the Sunnah Regarding Them
Narrator(s): Abdul Malik bin 'Umayr al-Qabti عبد الملك بن عمير بن سويد القبطي, Jabir bin Samra, Muhammad bin Yahya bin Hiban محمد بن يحيى بن حبان, Ubaidullah bin 'Umar al-Qawariri عبيد الله بن عمر القواريري, Yahya bin Yusuf يحيى بن يوسف

“When the reciter says Amin, then say Amin, for the angels say Amin, and if a person’s Amin coincides with the Amin of the angels, his previous sins will be forgiven.”

Source: https://parallelquran.com/hadith/sunan-ibn-majah-585/