Musnad Abu Ya'la al-Mawsili 155:380

Nasr ibn Ali al-Jahdami narrated to us, Safwan ibn Isa narrated to us, from Bishr ibn Rafi, from the father of Abdullah ibn Abi Hurairah, from Abu Hurairah, who said: The people have abandoned "Amin." If the Messenger of Allah (may Allah bless him and grant him peace) recited "Not of those who have evoked [Your] anger or of those who are astray," he would say "Amin" until the first row could hear it.