What is the ruling on selling a commodity that was reserved by paying an advance, for an increase above its original price after its price has risen and the delivery date has arrived, but before it has been taken possession of?

If the question is about selling an item before taking possession of it, the answer is that if the item is food, selling it before taking possession of it is forbidden by consensus (ijma'). If it is not food, the preponderant view among scholars is also prohibition, due to the generality of the evidence. Therefore, it is obligatory not to sell an purchased item until after taking possession of it from the seller.

However, if the intent of the question is merely the permissibility of selling an item at a price that will increase, then that is permissible at any price agreed upon by both parties.