Narrated Abu Huraira (RadhiAllahu 'anhu):
Prophet of Allah (Sallallaahu 'alaihi wasallam) said:
"When the Imam says:
غَيۡرِ ٱلۡمَغۡضُوبِ عَلَيۡهِمۡ وَلَا ٱلضَّآلِّينَ
'Ghair-il-Maghdubi 'Alaihim Walad-Dallin
(i.e. not the path of those who earn Your Anger, nor the path of those who went astray (1.7)),
then you must say, 'Ameen', for if one's utterance of 'Ameen' coincides with that of the angels, then his past sins will be forgiven."
[Sahih Bukhari - Book 60 - Hadith 02]
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