In his response to this, Dr.Monzer Kahf, a prominent economist and counselor said that
‘selling goods and services like auditing to banks is permissible. However, any thing that is exclusively used for writing an interest-based contract is not permissible. The Prophet (peace and blessings be upon him) said that the Wrath of Allah is on the taker, giver, writer and the two witnesses of Riba. Bank interest is Riba no doubt about it.
On the other hand, working in a bank in any job that does not require you to write a loan contract or any part of it is permissible.
Therefore, there is nothing wrong for any company to do a service for a bank as long as this service is not exclusively used for writing an interest-based contract.’