Prayer valid without audible sound?

In the stated case, if your tongue and lips were moving while reciting the Tashahhud and giving the Salam, and the letters were correctly articulated with your tongue, but you could not hear your own voice, then according to one reliable (recognized) view of the Hanafi jurists, your prayer is valid. However, the more correct and precautionary view is that, in recitation and similar matters, there should be at least enough sound that a person would normally be able to hear his own voice under ordinary circumstances.

Therefore, in the future, recite the Tashahhud, Salam, and other adhkar of the prayer at a volume that allows you to hear yourself. However, it is not necessary to repeat the prayer in question, provided that the words were actually articulated with the tongue and were not merely imagined or recited in the heart.

And Allah knows best.