Question: 

My friend recently asked why we Shias do not say ‘aameen’ when performing Salat (prayers). One website says that it is because there are not enough proofs that the Prophet used to do so in his prayers. Are there any other reasons?

Answer:

The reason is that the Prophet never did this and therefore it is not part of Salat. We have no proof that the Prophet ever did or approved this. Deliberately adding something to prayer which is not part of prayer, voids the prayer.

Furthermore,  آمين (aameen) is not a word of Quran. In fact, it may not be originally Arabic and in the first and 2nd rak’at we are reciting Quran, that’s why its called القراءة (al-qiraa-ah), so nothing which is not in the Quran should be in it.

Answered by: Sheikh Mansour Leghaei