Does the work of a chemical engineer in treating water and air conditioning for hotels—that contain abominations such as the presence of bars, fornication, and mixed swimming pools—constitute aiding in the unlawful, and does the ruling "rather, you are among those who wrong themselves" apply to him?

It is forbidden to cooperate in sin and aggression. Therefore, hotel maintenance is prohibited from any work that assists in the forbidden, such as maintaining a place for drinking alcohol, brothels, or mixed-gender swimming pools. Thus, one must limit their work to maintaining things that do not aid in the forbidden. If the work involves assisting in immoral acts and transgressions, one must avoid it and seek other employment, because "whoever fears Allah, He will make for him a way out of every difficulty and a relief from every distress, and provide for him from where he does not expect." The wages obtained from forbidden work may not be kept; rather, they must be disposed of by spending them on general Muslim welfare, such as sponsoring orphans.