Is it permissible for an engineer to accept payment for designing or decorating a mixed-gender café where shisha is served and cigarettes are smoked? If it is impermissible (haram), is it permissible to complete it and donate the payment if it is not possible to withdraw after having promised or started the work?

If vice and disobedience usually prevail among the patrons of a cafe, then it is not permissible to assist in its establishment and furnishing, because means are judged by their ends, and "that which leads to the forbidden is forbidden." This is in accordance with the Almighty's saying: "And cooperate in righteousness and piety, but do not cooperate in sin and aggression" (Al-Ma'idah: 2). The issue is not with taking the wages, but rather with completing the establishment and furnishing of the cafe. This falls under the principle of blocking the means (sadd al-dhara'i'), as the Shari'ah has blocked the means that lead to the forbidden, because they are instruments that lead to it. Abandoning this work is considered advice to the cafe owner and an enjoining of good and a forbidding of evil.