What is the ruling on purchasing rebar by paying the full amount to the factory without specifying a time for delivery, while retaining the option to back out of the purchase?

It is permissible to purchase iron through a Salam contract or an Istisna' contract. The conditions for a Salam contract are: the commodity must be precisely described, the full price must be paid at the contracting session, and the delivery date must be specified, based on the Prophet's (PBUH) saying: "Whoever pays in advance (for something), let him pay in advance for a known measure, a known weight, for a known term."

As for Istisna', it requires specifying the delivery date and describing the manufactured item. It does not require paying the full price at the time of contracting.

If the delivery time is not specified, the contract is invalid. Also, the condition that the buyer can withdraw from the purchase at any time invalidates the contract, because a contract cannot be made conditional, and the option of revocation (khiyar al-shart) in a Salam contract is not permissible according to the majority of jurists.

To correct the transaction, the delivery date must be specified, and the condition of withdrawing at any time must be removed.