Does the prohibition of a thing necessitate its invalidity?

Question:
Does the prohibition of a thing necessitate its invalidity?

Answer:
A: It may necessitate invalidity, and it may not. The prohibition of selling necessitates the invalidity of the sale, and the prohibition of praying at a specific time—such as the time of prohibition—without a cause invalidates the prayer.
Q: It invalidates it?
A: Yes, if one prays during the time of prohibition without a cause, the prayer is invalid.
Q: Does the prohibition necessitate invalidity? Or does the prohibition (tahrim) necessitate invalidity?
A: Prohibition (tahrim) necessitates invalidity, except where evidence indicates that it is not prohibited and not invalid.