Thus, there are four cases:
- That which is irrigated entirely at expense.
- That which is irrigated entirely without expense.
- That which is irrigated half by means involving expense and half by other means.
- That which is irrigated by means involving expense and by other means, in unequal proportions.
If it is irrigated entirely at expense, then half of a tenth is due; if it is irrigated entirely without expense, then a tenth is due; if it is irrigated equally by both methods, then three quarters of a tenth is due; and where the proportions differ, the method that is more beneficial is taken into account.
His statement, “and when it is unknown, a tenth is due,” means: if the proportions differ and we do not know which of the two methods is more beneficial, then a tenth is to be taken into account, because this is the more cautious course and more effectively clears one’s liability. Whatever is more cautious is therefore more appropriate.
If someone were to say: How can this be the more cautious course when it obligates people to do something for which we have no certain evidence that it is obligatory?
The response is that the basic principle is that zakah is obligatory, and that a tenth is due unless we know that it was irrigated at expense, in which case half of it is waived. Here, however, we do not know; we are unaware of which method is more beneficial. Thus, the cautious course is to require a tenth.
His statement, “When the grain hardens and the fruit begins to ripen, zakah becomes obligatory”: it has previously been mentioned that one condition is for the niṣāb to be owned by him at the time zakah becomes due.
Thus, the time when it becomes due is “when the grain hardens,” meaning that the grain becomes firm and