In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
In his response to your question, Prof. Dr. Monzer Kahf, Professor of Islamic Finance and Economics at Qatar Faculty of Islamic Studies, states:
Riba is definitely one of the most sinful violations of the Allah that invokes a war from Allah and Hi Messenger (peace be upon him).
Working in a riba institution needs more details as the Prophet declared four things prohibited in relation to riba: taking it, giving it, writing it and being a witness to it.
There is definitely a lot of wisdom in understanding this Hadith because if a job in a bank does not include writing riba, signing it, drafting it or being a witness to it, this job itself is not prohibited and the money received as salary from such a job is not haram because we do not look beyond the mutual relationship between a worker and the institution to argue the sources of funds of the institution.
Besides, not all sources of funds of a bank are riba. There are many commissions and fees that are not haram and that make only payments for services a bank offers.
On the other hand, we must realize that working in a bank, even when it does not require a worker to write or be a witness to a riba contract is part of the institution and the institution (bank) needs all such side jobs to work.
This means that any worker in a bank is definitely helping a riba-based institution although the job of such worker may not be itself haram because it may have no relation to taking Riba, giving it, writing it or being a witness to it.
If the job of this gentleman does not require him to write, negotiate or sign a riba contract, his job and income is not haram. It’ss only being a part of the institution is an issue that does not make it haram but out of religiosity, some of us may like to stay away from it. Then you make your own decision.
Almighty Allah knows best.