Sayyed Mohammad Al-Musawi, Sayyed Mohammad al-Musawi is originally from Iraq and heads up the World Ahlul Bayt Islamic League in London. Other than being involved in various humanitarian projects, he frequently responds to... Answered 1 year ago

Saying Ameen after Sura Al-Hamd is a Bid'ah came from non Muslims. Authentic Hadeeth from Muhammad al-Halabi: I asked Aba Abdillah (Imam Jafaria Al-Sadiq) (AS):  Can I say Ameen after Sura Al-Hamd?  Imam Al-Sadiq replied: No. (Al-Wasaa'il, 4:450).

Shaikh al-Sadouq stated in his book Al-Faqeeh 1:390 that: It is not allowed to say Ameen after reciting Al-Fatiha, because it is said by the Christians ( Nazareths). 
Shaheed al-Awwal said in his book al-Thikra 3:345 : Saying Ameen after Sura Al-Fatiha is not permissible and it invalidates the Salah. It is Bid'ah.

Wassalam.