The Messenger of Allah ﷺ addressed us, explaining our practice and teaching us how to pray. He said, "When you pray, straighten your rows, then let one of you lead you. When he says the takbir, say the takbir. When he says, 'Not those who have earned anger, nor those who have gone astray' [Fatihah 1:7], say 'Ameen,' and Allah will respond to you…"
إن رسول الله ﷺ خطبنا فبين لنا سنتنا، وعلمنا صلاتنا، فقال: إذا صليتم فأقيموا صفوفكم، ثم ليؤمكم أحدكم فإذا كبر فكبروا، وإذا قال: {غير المغضوب عليهم ولا الضالين} فقولوا: آمين، يجبكم الله…
Muslim narrated it in the Book of Prayer (404) through several routes from Abu Awana, from Qatada, from Yunus bin Jubayr, from Hittan bin Abdullah Raqashi, who said, "I prayed with Abu Musa Ashari a prayer..." and he related the hadith in full.