Is saying 'Amin' (So be it) after Al-Fatiha a Sunnah for the Imam and the follower (Ma'mum)?
Chapter on the Description of Prayer
Al-Mughni
Book of Prayer
Primary text
Saying 'Amin' after the Imam completes Al-Fatiha is a Sunnah for both the Imam and the follower. This position is held by Al-Thawri, 'Ata', Al-Shafi'i, Ishaq, and the People of Opinion (Ashab Al-Ra'y). Evidence supporting this includes the narration from Abu Hurairah that the Prophet commanded followers to say 'Amin' when the Imam says 'Amin,' promising forgiveness for those whose 'Amin' coincides with that of the angels. Furthermore, Wael ibn Hujr narrated that the Prophet said 'Amin' loudly after saying {nor of those who go astray} (Al-Fatiha 1:7). Bilal is also reported to have cautioned the Prophet not to precede him in saying 'Amin.'
Supporting text
The Malikis argue against the Imam saying 'Amin' based on a narration from Abu Hurairah stating that when the Imam finishes, the followers should say 'Amin,' implying the Imam does not say it. They interpret the narrations about the Imam saying 'Amin' as merely instructing the followers on when to say it, which should coincide with the angels' 'Amin' and the Imam's 'Amin.'