Is it permissible to sign papers and pay a down payment to purchase a car from a bank before the bank owns or possesses the car?

Pre-signing a promise to purchase along with taking an earnest deposit as a guarantee is permissible according to Islamic law. This is known as murabaha lil-amir bi al-shira' (cost-plus sale for a party ordering a purchase), provided that the bank bears responsibility for the destruction of the commodity before delivery and the liability for returning it due to a hidden defect. The signing and payment of the earnest deposit do not affect the permissibility of the transaction as long as it remains within the realm of a promise. It is permissible to take an earnest deposit on condition that nothing is deducted from it except for the actual damage incurred upon reneging. However, if the signing and the earnest deposit represent the purchase contract itself, then the contract is void because the bank is selling what it does not own, as the Prophet (peace be upon him) said: "Do not sell what you do not possess."