What is the ruling on the work of a contractor or an electrician who deals with banks to receive payment for their services in buying and selling homes, knowing that the bank deals with interest (riba) with the buyer?

It is permissible to complete the agreed-upon services with the bank (such as construction and electrical wiring) and receive payment for them, even if the transaction between the bank and the service seeker is prohibited. The sin falls upon them, and nothing accrues to the contractor, as he is performing a permissible service that does not involve aiding in a forbidden act.