What is the ruling on purchasing a car from an agent who does not currently own it, but will buy it after the buyer pays the money and specifies the features? Is this considered a salam (forward) sale in specified items, or selling what one does not own? And does it resemble selling dates described by specification (dhimmah)?

It is permissible to engage in a Salam (forward) sale of cars if they are described with specifications that prevent dispute, along with the fulfillment of the known conditions of Salam, such as specifying the term, the price, and delivering the capital at the contracting session.

It is not permissible to sell a specific car before owning it, which is selling what one does not possess, a practice that is prohibited.

The sayings of scholars regarding "Do not sell what is not with you" revolve around prohibiting the sale of specific assets not owned due to gharar (uncertainty), while a Salam sale (selling a described item that is a liability) is permissible under its conditions.