Unity of genus and kind (ittihad al-jins wal-naw')

Jins is a kind of any thing and is broader than naw', a narrower sort; ittihad is the merging of two things until they become one. ¹ The schools differ on what unity of genus means. ¹ It is a condition for a valid zakat payment on livestock other than camels when the payment comes from the same genus as the nisab, and it restricts some transactions. ²

For the Hanafis it is unity of the specific name and of the purpose; for the Malikis, equal or close benefit; for the Shafi'is, the two items share one specific name, so wheat and barley are two genera; for the Hanbalis, kinds that share one root even when their purposes differ. ^{1 2} For the Malikis, gold and silver are two genera in sales but one genus in zakat. ² For the Hanafis unity of genus is part of the cause of ribawi sales, the cause having two parts, genus and measure; for others it is a condition. ²

In zakat on livestock other than camels, the majority of schools allow paying from the same genus as the nisab, of the nisab's amount or more; a payment from a different genus is not valid. The Hanafis allow paying the value whether or not the genus is the same. ² In the sale of a ribawi good for one of its own kind, unequal exchange is forbidden by agreement and the sale is void; equal exchange hand to hand is valid. ²

Jurists treat unity of genus in zakat (livestock, crops and money), in hajj (unity of the expiatory payment), in riba, in salam, in set-off, and in claims. ²