قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ : " إِذَا قَالَ أَحَدُكُمْ : آمِينَ وَالْمَلائِكَةُ فِي السَّمَاءِ آمِينَ، فَوَافَقَ إِحْدَاهُمَا الأُخْرَى غُفِرَ لَهُ مَا تَقَدَّمَ مِنْ ذَنْبِهِ "
And the Messenger of Allah, peace and blessings be upon him, said: "When any one of you says Ameen, and the angels also (at the same time) in the heavens (say Ameen), such that one’s Ameen coincides with the Ameen of the other, then all his previous sins will be forgiven."