Is it permissible for Zayd to purchase a machine in installments from a customer, after having sold it to him for cash, knowing that the machine is still under manufacture?

The jurists differed on the ruling concerning the manufacturing contract (Istisna'). The Hanafis permitted it with conditions that remove ambiguity, such as specifying the material, description, and quantity of the manufactured item. As for the majority of jurists, they equated it with the Salam contract and stipulated for it the conditions of Salam, including the full payment of the price at the contracting session. Otherwise, the contract would be invalid because not paying the full capital at the contracting session is considered from the category of "ta'meer al-dhimmatayn" (making two liabilities effective), which is forbidden. Based on this, the aforementioned contract is not valid due to the non-payment of the price of the manufactured item at the contracting session.