Sheikh Sâmî al-Mâjid
The work that people do for commercial banks can be divided into two broad categories: work that directly relates to the bank’s interest transactions and work that does not.
Working in a bank as a teller or in any other capacity where one deals directly with bank's usurious transactions is unlawful. The person who engages in such work makes himself deserving of the curse mentioned by Allah’s Messenger (peace be upon him), since that person is considered one of those who records the interest transaction.
The Prophet (peace be upon him) said: “Allah curses the one who consumes interest, the one who pays it, the one who draws up the contract, and the witnesses to the contract, then he said they are same (in sinfulness) ” [Sahîh Muslim]
The money earned by a person working in a bank in such a capacity is unlawful money, since the money is earned through means that are inherently unlawful.
The case is different for a person who works for a bank in some other capacity, not directly involved in the bank’s interest transactions, like someone who works in personnel management. Even though such work does not entail direct involvement in interest, it still entails helping others in their unlawful activities, so the employee still incurs sin for the help that he is giving the bank.
Allah says: “Help ye one another in righteousness and piety but help ye not one another in sin and rancor: fear Allah: for Allah is strict in punishment” [Sûrah al-Mâ’idah: 2]
However, the money earned by the person is lawful money, since the job is essentially lawful in and of itself.
And Allah knows best.
Source: Islam Today