The prostration of forgetfulness is prescribed for one of three situations:
First: when something is unintentionally added to the prayer.
Second: when something is unintentionally omitted from the prayer.
Third: when the worshipper is unsure whether he has added or omitted something.
He prostrates for whichever of these three circumstances actually occurs, in the manner established by the texts, and not for every possible addition, omission, or doubt.
This prostration is legislated whenever its cause is present, whether the prayer is obligatory or voluntary, for the proofs are general in wording.
The first situation that calls for the prostration of forgetfulness is an addition in the prayer, which may consist either of extra movements or extra words.
- Extra movements: if the addition is of the same type as the prescribed acts—such as standing where one should be sitting, sitting where one should be standing, or performing an extra bowing or prostration—then, if it occurs unintentionally, he performs the prostration of forgetfulness. This follows the ḥadīth of Ibn Masʿūd: “If a man adds to or omits from his prayer, let him prostrate twice,” recorded by Muslim. An addition is reckoned, in effect, as a shortcoming in the overall form of the prayer, so the prostration is prescribed to make up for that deficiency.
Similarly, if a person unwittingly performs an extra rakʿah and does not realize it until he has completed it, he should perform the prostration of forgetfulness. If, however, he becomes aware of the extra rakʿah while still in it, he should sit down at once, recite the tashahhud if he has not yet done so, then perform the prostration of forgetfulness and end the prayer with salām.