What is the ruling when the price is a specific physical commodity (*'ayn*) or an exchange of goods for goods?
Chapter on Selling the Musarrah (Animal with milk retained in udder)
Al-Mughni
Book of Sales
Primary text
When the price is a specific commodity or an exchange of goods for goods, an impartial arbiter shall be appointed between them. The arbiter receives both items from them and then delivers them to the respective parties. This is because both the sold item and the price are specific objects to which rights are attached, and since each party has a vested right to immediate possession of what the other owes, both parties must be compelled to fulfill their obligation to the other.
Supporting text
A second narration attributed to Ahmad suggests the seller is always compelled to deliver the sold item irrespective of the nature of the price. The reasoning is that the sold item is what completes and finalizes the sale, thus it should be prioritized. Furthermore, since the price is not specific until named, it is treated like an unspecified item.