...Not (the way) of those who earned Your Anger, nor of those who went astray. (V.1:7)

Hadith Number 4475

setting

Narrated Abu Huraira

Allah's Messenger (ﷺ) said, "When the Imam says: '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."