How is salam (forward) selling permissible, even though the commodity is not in the seller's possession, and the Prophet, peace and blessings be upon him, forbade selling what one does not possess when he said: "Do not sell what you do not have"?

The prohibition mentioned in the Prophet's (PBUH) saying: "Do not sell what you do not possess" specifically concerns the sale of tangible assets owned by others, and the potential for uncertainty (gharar) and disputes that may arise from the inability to deliver.

However, if the sold item can be precisely described and its existence at the time of delivery is highly probable, such as in a salam sale, then it is permissible by the Qur'an and Sunnah. This is because it is not the sale of a specific item, but rather of a commodity that possesses the agreed-upon characteristics. Scholars did not stipulate the existence of the commodity in the seller's possession at the time of the salam contract; rather, they stipulated its likely existence at the time of delivery. The underlying reason for prohibiting the sale of some non-existent items is gharar (uncertainty), not mere non-existence.

The difference between the two is that in a salam sale, the seller is obligated to deliver the described commodity, which is a liability upon him, when the due date arrives, even if he has to purchase it from someone else. Whereas in the sale of a specific tangible asset, he is obligated to deliver that very asset, with no alternative.