To what extent is it permissible for Muhammad to sell a car to Zayd for a deferred price, then for Zayd to appoint Muhammad to sell it on condition that the money be returned to Zayd, with Zayd having the option after three months between paying the price or returning the car?

The transaction mentioned can be interpreted in two ways: First, the seller sells the car and stipulates that the price be paid within 3 months, otherwise the sale is canceled and the car is returned. This is a valid condition known as "cash option" (khiyar al-naqd). Second, the seller stipulates that the amount be paid within the specified period or a car similar to it be returned. This is impermissible because it involves gharar (uncertainty) due to the fluctuation of the price between a monetary sum and a car. As for the buyer authorizing the seller to sell the item he purchased, there is no objection to it.