Sunan an Nasai
925
Sahih+2

It was narrated that Abu Hurairah said:"The Messenger of Allah (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

SahihAbu Ghuddah
SahihAl-Albani