Is it permissible to work as a sales representative in a car showroom where a commission is received for bringing the client to the bank to pay for the car in installments, with the client's knowledge of the bank they desire?

If the work done for personal gain during official working hours, specifically directing customers to banks through an exhibition, is considered, this is explained in Fatwa No. 113793. Guiding customers to non-Islamic banks and facilitating their prohibited transactions is a form of forbidden cooperation, whether for a fee or without one. A commission for a forbidden benefit is not permissible, and its possessor must dispose of it by spending it on charitable causes. However, this does not initially legitimize engaging in the forbidden transaction.