What is the ruling of Islamic law regarding an agreement between a borrower and a building contractor to take a portion of the building loan in cash after the amount has been transferred from the bank to the contractor?

The method used by Islamic banks for building houses is called "parallel Istisna'a" (manufacturing contract). In this, the bank agrees with the client on the specifications and price of the house, and then agrees with a contractor on the same specifications. It is permissible for the client to agree with the contractor to give him a portion of the money, because the manufacturer owns the money that the bank has handed over to him. However, it is not permissible to pay an increase to the contractor in exchange for this money, otherwise it would be prohibited usury (riba). Similarly, this is not permissible if it leads to harm for the bank, based on the Prophet's (PBUH) saying: "There should be no harm nor reciprocal harm."