صَحِيحُ مُسْلِمٍ
Sahih Muslim 410 d
The Book of Prayers
Saying "Sami'a Allahu liman Hamidah," Rabbana wa lakal-hamd," and "Amin"
حَدَّثَنَا عَبْدُ اللَّهِ بْنُ مَسْلَمَةَ الْقَعْنَبِيُّ، حَدَّثَنَا الْمُغِيرَةُ، عَنْ أَبِي الزِّنَادِ، عَنِ الأَعْرَجِ، عَنْ أَبِي هُرَيْرَةَ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم إِذَا قَالَ أَحَدُكُمْ آمِينَ . وَالْمَلاَئِكَةُ فِي السَّمَاءِ آمِينَ . فَوَافَقَتْ إِحْدَاهُمَا الأُخْرَى غُفِرَ لَهُ مَا تَقَدَّمَ مِنْ ذَنْبِهِ .
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 synchronises with (that of) the other, all his previous sins are pardoned.
Sahih Muslim, 410 dSahihصحيح