Is it permissible to design air conditioning systems for hotels, banks, prisons, places that contain swimming pools (such as clubs and villas), in addition to saunas, beauty salons, and health clubs that offer massage services?

The authoritative fatwa according to us is that it is not permissible to design air conditioning and the like for places designated for committing forbidden acts, such as interest-based banks or gambling clubs, due to the Almighty's saying: "And do not cooperate in sin and aggression." As for places that are not designated for forbidden acts, even if forbidden things are displayed therein, there is no harm in designing air conditioning for them, and this is not considered forbidden assistance.