Abu Harare reported: The Messenger of Allah ﷺ said: When anyone amongst you utters Amin and the angels In the heaven also utter Amin and (the Amin) of the one synchronizes with (that of) the other, all his previous sins are pardoned.
The hadith also teaches us about forgiveness and mercy from Allah. Even if we make mistakes or sin, Allah will still forgive us if we sincerely repent and ask for His forgiveness through prayer. We should never give up hope or feel like our mistakes are too big for Allah to forgive because He is always willing to accept our repentance if we are sincere about it.