Dr. Monzer Kahf, a prominent economist and counselor, states the following: “Although it is not the best kind of job in the world from the Shari’ah point of view, it is not forbidden to work for a conventional bank, whether it is investment or commercial as long as one does not write or fill in applications of interest-based contracts.
The Prophet (peace and blessings be upon him), forbade taking Riba, giving it, writing its contract/transaction and being a witness to it. Jobs that do not involve any of these are not forbidden, even if you give advice to customers about which kind of transaction/contract may be better for them.”