Is it permissible to contract for future delivery (salam) of measured goods by weight instead of measure?

Primary text

The primary ruling is that a contract of salam (future delivery) for goods that are ordinarily measured by volume (kayl) must be contracted using volume, and similarly, goods ordinarily weighed must be contracted using weight. This view is supported by Al-Athram's narration from Ahmad, which indicates that salam in dates must be by measure (kayl) even if the people are unfamiliar with measuring. Al-Qadi and Ibn Abi Musa support this, arguing that since the commodity's quantity must be known, it cannot be fixed by a method other than its original fixed measure, similar to exchanging damp goods for one another. Furthermore, fixing the agreed upon amount using a measure other than its original one invalidates the contract, like contracting for a measured fabric by weight.