Scholars agree that various kinds of fruit can be combined even if their quality is different – that is, excellent or bad in quality. Different kinds of raisins may also be combined together, and so can the various kinds of wheat and cereals.
They also agree that merchandise and its cash value received can be combined. Ash-Shaf’i allows combining goods and cash only when purchased because the nisab is calculated upon that. Scholars also do not allow the combination of certain categories with others in order to attain a nisab, with the exception of grains and fruits. That is why one category of animals cannot be combined with another. For example, camels cannot be added to cattle to complete a nisab, nor can fruit be combined with raisins.
Scholars have different points of view in regard to combining various types of grains with one another. The best and the most correct opinion is that no two things can be combined to calculate a nisab. The nisab must be considered on every category by itself. This is because there are various categories and many kinds. Therefore, barley cannot be added to wheat, nor can the latter be added to the former, which is also true of dates and raisins, and chickpeas and lentils. This is the opinion of Abu Hanifah, ash-Shaf’i, and Ahmad, according to one of the reports. Most of the early scholars hold this opinion.
Ibn al-Munzhir says that most scholars concur that camels cannot be combined with cattle or sheep, or cattle with sheep, nor dates with raisins. Thus, there can be no combining of different kinds of produce or animals. Those who allow such a practice do it without any authentic proof.