Is it permissible to specify a type of commodity within a genus and then except a different type from the same genus in a debt obligation?
General Chapter
Al-Mughni
Book of Acknowledgment of Rights
Primary text
It is not permissible to specify one type of commodity belonging to a genus and then except another type of that same genus in a debt obligation, such as stating, 'I owe you ten Sa' of Barniy dates, except three Sa' of Ma'qili dates.' This ruling is maintained because the stated principle prohibits such specific exception within a defined category. This situation differs from exceptions concerning gold and silver ('ayn and waraq) because the value of one type of date is not known from the other, nor can one type be used to substitute for the other.
Supporting text
There is a possibility, according to the opinion attributed to Al-Kharqi, that this practice is permissible due to the close nature and similarity of the intended purposes between the two types of dates, likening them to gold and silver. However, the former position is stronger because the valid rationale concerning gold and silver does not apply to this scenario.