Does merely concluding a legitimate contract with an Islamic bank absolve one of responsibility despite the existence of irregularities, and is the legitimacy of the transaction affected by Islamic banks placing financial collateral in usurious banks, and is the existence of Sharia supervision sufficient to absolve one of responsibility?

The fundamental principle for Islamic banks is to adhere to Sharia guidelines. However, if a clear Sharia violation is found in a particular transaction, it is impermissible to engage in it. It is not sufficient for a bank to be merely labeled "Islamic" or to have a Sharia board. The dealings of Islamic banks with the central bank and other banks are sometimes necessary and do not affect their Sharia compliance as long as the dealings are within permissible limits or out of necessity. As for Sharia supervision, if it is scientifically and religiously qualified, an ordinary Muslim may follow its rulings.