Is it permissible to work in tax departments? And is there a ḥadīth that prohibits a Muslim from working as a "tax collector or overseer" in a situation where Islamic law is not applied?

It is permissible for the state to impose taxes to provide essential services if the public treasury has been depleted, provided that this is not without return or if there is sufficient in the public treasury; otherwise, it would be unlawful (haram). A "sahib maks" (unjust tax collector) will not enter Paradise. Working in tax departments depends on the nature of the collection: if it adheres to Islamic law and the funds are spent for the benefit of Muslims when the treasury is empty, then it is permissible to work in it, provided there is justice and avoidance of oppression and bribery. However, if the state imposes taxes without return, or if the work regulations contradict Islamic law, then neither collection nor working in it is permissible, due to Allah's saying: "And do not cooperate in sin and aggression." There are also hadiths warning against being a ruler, a scribe, a chief, a policeman, or a tax collector, such as his (peace be upon him) saying: "You have succeeded, O Qudaim, if you die and have not been a ruler, nor a scribe, nor a chief." A Muslim must seek what is lawful and avoid what is unlawful and doubtful. Therefore, one should not work in these departments except after verifying that their systems and laws conform to Islamic law.