Sayyiduna Wa'il bin Hujr al-Hadrami (may Allah be pleased with him) said: When the Messenger of Allah (peace and blessings be upon him) recited "nor of those who go astray," he would say "Amin," raising his voice with it.
Hadith Referenceالمعجم الكبير للطبراني / باب الواو / 18331