Our purpose is to address those questions about which the Sacred Law is virtually silent, except in a few instances—either because they are well-known and serve as foundational precedents for other rulings, or because they arise with great frequency.

The five occasions on which the Messenger of God—peace and blessings be upon him—experienced forgetfulness are:

1. He rose for a third rakʿah after two, as reported in the ḥadīth of Ibn Buhaynah.
2. He gave the closing salām after two rakʿahs, as related in the ḥadīth of Dhū al-Yadayn.
3. He prayed five rakʿahs, as found in the ḥadīth of Ibn ʿUmar recorded by Muslim and al-Bukhārī.
4. He ended the prayer with salām after three rakʿahs, as stated in the ḥadīth of ʿImrān ibn al-Ḥuṣayn.
5. He performed the prostration on account of doubt, as mentioned in the ḥadīth of Abū Saʿīd al-Khudrī, to be discussed later.

The jurists disagreed about why the prostration of forgetfulness (sujūd al-sahw) is obligatory. One opinion—the better known—holds that it is required for both additions and omissions. Another opinion, adopted by the Ẓāhirīs and by al-Shāfiʿī, holds that it is required simply because forgetfulness itself has occurred.

Chapter Three
Concerning the Utterances and Acts That Call for the Prostration of Forgetfulness

Those who oblige a prostration for every omission or addition that occurs in the prayer through forgetfulness agree that the prostration applies to the Sunan of the prayer, not to its obligatory pillars (farāʾiḍ) and not to its merely recommended acts (raghāʾib).

Regarding the raghāʾib, nothing is required when they are forgotten in the prayer—unless more than one recommended act is omitted. Thus Mālik holds that no prostration is due for forgetting a single takbīrah, whereas it is required if more than one is missed.

As for the obligatory pillars, nothing can compensate for them except performing them themselves. They must be rectified when the lapse is of a kind that does not necessitate repeating the entire prayer, in line with the earlier discussion of what does and does not mandate repetition—namely, when someone has left out one of the pillars of the prayer.

With regard to the prostration of forgetfulness for additions, it is required whenever something extra is inserted, whether into the obligatory elements or into the Sunan of the prayer. On this rule there is no disagreement among them; their divergence stems only from their differing classifications of particular components—whether a given element is obligatory or not, Sunnah or not, or Sunnah as opposed to merely recommended.

For example, according to Mālik one does not prostrate for omitting the qunūt because, in his view, it is merely recommended, whereas according to al-Shāfiʿī one does prostrate because, in his view, it is a Sunnah. This, as you will have noted, ties back to their earlier dispute over what counts as Sunnah, as obligation, or as recommendation—and according to Mālik