Is the aforementioned dealing with the bank regarding the Istisna' (manufacturing) contract and the legality of the specified profits, the ruling on dealing with a bank whose original capital may be unlawful, and the Sharia responsibility for the bank's hidden transgressions, permissible in Sharia?

It is permissible to conclude a contract with the bank in an Istisna’a (manufacturing) transaction if the contract between the customer and the bank is separate from the contract between the bank and the contractor, and each of them is Islamically compliant. Thus, the Istisna’a contract between the customer and the bank is permissible and binding on both parties under certain conditions, including: specifying the manufactured item and its characteristics, setting a deadline, allowing for the postponement or installment of the price, and permitting the stipulation of a penalty clause.

As for the contract between the bank and the contractor, if the bank purchases the materials, it is a lease contract (Ijara). If the contractor provides the materials, the contract is a permissible parallel Istisna’a under certain conditions. There is no blame on the questioner for engaging in this transaction as long as their contract with the bank is valid, and they are not harmed by any transgression on the part of the bank or suspicion regarding its funds, because a person is only responsible for their own actions.