What is the recompense for one who forbids what is lawful, and is it permissible for a husband to prevent his wife from going to a religiously permissible swimming pool based on a fatwa that prohibits it?

One must differentiate between prohibiting what Allah has made lawful, which is among the greatest major sins, and the differing opinions of muftis and jurists on jurisprudential issues, which is a permissible and legitimate difference.

A Muslim should be open-minded regarding scholarly differences and acknowledge their esteemed status.

The differing opinions of muftis concerning a woman swimming in public women-only pools falls under the second type—a permissible difference among jurists—and not under the category of prohibiting what Allah has made lawful, as there is no definitive text on this matter.

As for the woman who inquired, she must obey her husband if he forbids her from going to the aforementioned pool, because obedience to him is obligatory upon her, and his permission is a condition for the permissibility of her swimming in the pool.