Whenever the Messenger of Allah ﷺ recited "nor of those who go astray" [Fatihah 1:7], he would say, "Ameen," raising his voice with it.
حدثنا محمد بن كثير أخبرنا سفيان عن سلمة عن حجر أبي العنبس الحضرمي
كان رسول الله ﷺ إذا قرأ {ولا الضالين} قال آمين ورفع بها صوته
[Sahih] Reported by Tirmidhi, Prayer, Chapter on what has been said regarding saying "Ameen," no. 248, from the hadith of Sufyan Thawri, with this wording. He said, hasan, and Daraqutni graded it sahih (1/334), as did Ibn Hajar (Talkhis Habir 1/236) and others.Yahya Qattan reported it from Thawri with this wording, and he would only report from him what he explicitly stated to have heard directly.