The following rules apply to items that are not sold by weight, but sold either by measurement or counting. If a particular type of item is exchanged for the same type of item, e.g. guavas are exchanged for guavas, or oranges are exchanged for oranges, or a fabric is exchanged for similar fabric, then in all these cases it is not a prerequisite for both the items to be equal. It is permissible to have some difference. However, it is waajib for the transaction to be executed there and then.
If the item that is being exchanged is different from the other item, e.g. guavas are exchanged for oranges, wheat is exchanged for guavas or a fine fabric is exchanged for a coarse fabric, this will be permissible under all circumstances. It is not waajib for both the items to be equal nor is it waajib to execute the transaction there and then (i.e. it is permissible to take, for example, the guavas now and give the oranges later on).