According to Nyaya, the classical Indian school of logic, which fallacy is committed in the following argument: Sound is eternal because it is produced?

The argument commits the viruddha fallacy, the contradictory middle.

Sound is eternal because it is produced offers being produced as the reason.

But whatever is produced is in fact non-eternal, not eternal.

So the middle term proves the very opposite of the intended sadhya.

A reason that establishes the contradictory of the thesis is viruddha.