Dr. Monzer Kahf, Scholar in Islamic Economics & Financial Expert, states the following: “All of us know that bank interest is a kind of Riba which is prohibited in the Shariah. It is also prohibited to give it, receive or take it, write its contracts and be a witness on them. Hence, any job that requires a Muslim to make a contract of Riba or be instrumental in making it such as negotiating it with the customer, getting it signed or signing it on behalf of the bank and other jobs related directly to making a Riba-based contract with regards to deposits or financing in a Reba based bank is prohibited.
There are jobs in banks that do not relate directly to Riba such as guards, tellers, treasurers, research, buildings and machines maintenance, etc., I personally quote two of the greatest Muslim scholars’ views regarding that as follows:
His eminence Sheikh Muhammad al-Siddiq al-Darir of Sudan and His eminence Sheikh Muhammad al-Mukhtar al-Sallami of Tunis are of the opinion that such jobs are not included in the prohibition. However, they maintain that jobs which support the Riba-based operations are prohibited.”