or an addition.

The fourth category: uncertainty concerning an addition. The author alluded to this in his statement:

“...or an addition.” That is, if he is uncertain whether he added something to his prayer—in which case he would be required to perform the prostration for forgetfulness—or whether he did not add anything—in which case no prostration is due—then he does not prostrate, because he is uncertain about the cause requiring the prostration, and the basic presumption is that it did not occur.

For example, during the final tashahhud of the Zuhr prayer, he is uncertain whether he prayed five rak‘ahs or four. No prostration is required of him, because the rak‘ah was completed as the fourth without any uncertainty; the doubt only arose after he had moved beyond its proper place, and the basic presumption is that no addition occurred.

But if he becomes certain that he prayed five rak‘ahs, then he must perform the prostration for forgetfulness, because he is certain that he added something, and the prostration for forgetfulness is therefore obligatory.

The first case: if he is uncertain about an addition and then becomes certain of it, he must perform the prostration because of the addition.

The second case: if he is uncertain about an addition while performing the additional act, then it becomes clear that there was no addition, he must nevertheless perform the prostration according to the established position of the school (1), because he performed this rak‘ah while uncertain whether it was additional or not.

The third case: if he becomes uncertain about an addition after finishing, no prostration is required of him, because he is uncertain about the cause requiring the prostration, and the basic presumption is that it did not occur.

Thus, his statement, “...or an addition,” admits of two exceptions:

The first exception: if he becomes certain of the addition. Perhaps we may say that this does not need to be treated as an exception, because it is not a case of uncertainty; the author says, “because he is uncertain about the addition.”