All perfect praise be to Allah the Lord of the Worlds. May His peace and blessings be upon Prophet Mohammad and upon all his family and companions.
The fundamental Islamic principle regarding conditions stipulated by contracting parties in a sale contract is that they are valid unless they contradict the essence of the contract. Imam Al-Qalyubi of the Shafi'i school of thought stated: "To summarize, a condition in a contract can have five categories: either it ensures the validity of the contract, like stipulating the harvesting of fruit; or it aligns with its essence, such as delivery or the right to return due to a defect; or it relates to its benefits, like stipulating tasks such as writing or tailoring; or it serves no apparent purpose, such as eating Harisa (A kind of Arab sweets); or it contradicts the essence of the contract, such as prohibiting delivery of the goods. The latter invalidates the contract, unlike the former categories." [Hashiyat Al-Qalyubi on Kanz Al-Raghibin/Vol.2/P.224].
The Murabaha contract for the purchase orderer is a type of sale, and it is not permissible in Islamic law for the bank to stipulate a prohibition on selling the purchased item. This condition contradicts the essence of the sale contract because ownership of the item has already been transferred to the client (buyer). However, it is permissible for the bank to require that the purchased item be pledged as collateral in its favor. In such a case, the item cannot be sold after being pledged without the bank’s permission.
It is also not permissible for the client to pay any portion of the price to the original seller or to the bank. Instead, the client may pay a guarantee deposit, which is not considered part of the price.
Accordingly, it is not permissible, according to Islamic law, for the bank to stipulate a prohibition on selling the purchased item until the installments are fully paid, except if this is done in the form of a pledge (Rahn), in which case it is permissible with the bank's consent. And Allah The Almighty Knows Best.