Bismillah. Alhamdulillahi rabbil-'alamin was-Salatu was-Salam 'ala Sayyidil-Mursalin wa 'ala 'Alihi wa Sahbihi Ajma'in.
Takbir Tahrima is a fard (obligatory) rukn of Salah. But should it be said loudly? Or can it be said just by whispering (with very low voice) or silently (quietly)?
For both "yes" and no "answer" I need proof.
In case of "yes", what do dumb or deaf people do?
Special case that I am concerned with is that if Takbeer is said quietly (without making any sound) then Salah is not accepted. I'd like to know if this claim has base for. The concern comes from the fact that Takbir Tahrima is fard (obligatory) rukn of Salah.