Is it permissible to purchase a house by paying a sum of money from it to the bank as an usurious loan to its owner, knowing that this loan has no relation to the building of the house?

It is permissible to buy a house from its owner, even if the remaining amount due from the buyer will be paid to the bank on behalf of the seller. This does not affect the validity of the contract nor is it considered assisting in sin. It is important to note that one should not open an account in a usurious bank when paying installments; rather, it suffices to deposit the money into the seller's account only.