What is the ruling of Islamic law regarding a customer returning goods to the showroom and taking their value in cash, after having purchased them with financing from an Islamic bank, and is expiation (kaffarah) obligatory for the showroom owners and the customer if the transaction violates Islamic law?

We have clarified the impermissibility of what you have undertaken, which is the collusion with the one who orders the purchase by paying him the price and then returning the goods to him after completing the transaction with the bank. Every transaction intended to obtain money for more money at a later date is a usurious and forbidden transaction, because actions are judged by intentions, and indeed, every person shall have what he intended. This is what Sheikh Al-Islam Ibn Taymiyyah clarified. Among the conditions of Murabaha (cost-plus financing) in banking is that the intention of the transaction should not be to circumvent usury, as Sheikh Yusuf Al-Shubaili mentioned. Therefore, it is obligatory for you to repent to Allah Almighty, and for each of you to return what you took from the other. As for the bank, the transaction is not invalidated from its side because it does not know what you concealed. For every condition that invalidates a contract by being mentioned, it also invalidates it by intention. However, for one who is ignorant of the other party's intention, the contract is not invalidated from his side, as Sheikh Ibn Uthaymeen stated.