Reference: Liqaa. al-Baab al-Maftooh v68 p188
Question: If a person finished reciting soorah al-Faatihah in the quiet prayer (zhuhr and 'asr), should he say 'aameen' or not?
Response: When he finishes [reciting Soorah] al-Faatihah, he should say “aameen” in [both] the quiet and audible prayers, whilst doing so audibly [only] in the audible [fajr, maghrib and 'ishaa] prayers.
