What is the ruling on working as a mortgage consultant in a usurious bank while knowing its impermissibility, and is it permissible to transfer to the deposits department in the same bank believing its transactions to be lawful? What is the ruling on working in schools that deal with borrowing and loans? And does unlawful money become lawful if a person who is unaware of its impermissibility takes it? What is the ruling on zakat organizations dealing with money that may be unlawful?

Firstly: It is not permissible to work in interest-based banks, even if the work itself is not interest-based. This is because it constitutes assistance and strengthening of these institutions that are based on usury. The fatwa of the Permanent Committee (for Scholarly Research and Ifta) has stipulated this, based on the Almighty's saying: "And do not cooperate in sin and aggression."

Secondly: It is permissible to work in a school, whether as an employee or a teacher, even if the school takes out interest-based loans. This is because it does not fall under the category of cooperating in sin. Ali ibn Abi Talib worked for a Jew known for usury.

Thirdly: Unlawful wealth is of two types: 1. Unlawful in itself (such as usurped or stolen property): This must be returned to its owner. It is not permissible for anyone to sell anything to someone who buys it with such money if they are aware of its nature. 2. Unlawful due to its earning (such as wages from prohibited work): This money is unlawful only for its earner. It is permissible for anyone to whom it is transferred through a permissible means (such as a gift or wages) to benefit from it. Therefore, there is no harm for the restaurant owner in selling food to someone whose money is unlawful due to its earning, and he is not required to ask customers about the source of their money. Similarly, charitable organizations that accept Zakat are not required to question those who donate about the sources of their money, unless they know that it is unlawful in itself.