Sunan Abi Dawud, Hadith 932 ⓘ
Narrated Wa'il ibn Hujr: When the Messenger of Allah recited the verse "Nor of those who go astray" (Surah al-Fatihah, verse 7), he would say Amin; and raised his voice (while uttering this word).
حَدَّثَنَا مُحَمَّدُ بْنُ كَثِيرٍ، أَخْبَرَنَا سُفْيَانُ، عَنْ سَلَمَةَ، عَنْ حُجْرٍ أَبِي الْعَنْبَسِ الْحَضْرَمِيِّ، عَنْ وَائِلِ بْنِ حُجْرٍ، قَالَ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم إِذَا قَرَأَ { وَلاَ الضَّالِّينَ } قَالَ " آمِينَ " . وَرَفَعَ بِهَا صَوْتَهُ .
also referenced under: Hadith 932 (DarusSalam) & Book 3, Hadith 932 (USC-MSA)