Muhaqqaq Masala

If a person recites the Holy Quran so quietly in prayer that the letters are pronounced but he cannot hear it himself, then according to the Mufta-bihi (the position upon which the fatwa is given) opinion, his prayer will not be valid. This is because the limit of silent recitation (Sirr) is that a person recites in such a voice that he can hear it himself; mere movement of the tongue without sound is not considered as recitation. (Aham Masail / Vol: 1 / Pg: 30)