Yahya related to me from Malik from Abu'z Zinad from al-Araj fromAbu Hurayra that the Messenger of Allah, may Allah bless him and granthim peace, said, "When one of you says 'Amin' and the angels in thesky say 'Amin' so that one coincides with the other, his previouswrong actions are forgiven him." (IT)
App reference (IT): Book 3, Hadith 49 (IT)
USC-MSA web (English) reference: Book 3, Hadith 49 (IT)
Arabic reference (IT): Book 3, Hadith 196 (IT)