If anyone says Amin [during the Salat (prayer) at the end of the recitation of Surat Al-Fatiha] Sahih al-Bukhari 3236
Arabic hadith text
حَدَّثَنَا مُوسَى، حَدَّثَنَا جَرِيرٌ، حَدَّثَنَا أَبُو رَجَاءٍ، عَنْ سَمُرَةَ، قَالَ قَالَ النَّبِيُّ صلى الله عليه وسلم "رَأَيْتُ اللَّيْلَةَ رَجُلَيْنِ أَتَيَانِي قَالاَ الَّذِي يُوقِدُ النَّارَ مَالِكٌ خَازِنُ النَّارِ، وَأَنَا جِبْرِيلُ، وَهَذَا مِيكَائِيلُ "
Translation
Narrated Samura
The Prophet (ﷺ) said, "Last night I saw (in a dream) two men coming to me. One of them said, "The person who kindles the fire is Malik, the gate-keeper of the (Hell) Fire, and I am Gabriel, and this is Michael."