obligatory (wajib) adhkar (remembrances) (41), such as the glorification (tasbih) in bowing (ruku') and prostration (sujud), the statement: 'My Lord, forgive me' between the two prostrations, and the statement: 'Our Lord, and to You be the praise,' then one should not return to them after departing from their respective place, because the place of the remembrance is a pillar (rukn) that has already been performed in a sufficient and valid manner. If he were to return to it, it would be an addition to the prayer and a repetition of a pillar, and then he would be performing the remembrance in a bowing or prostration that is additional and not legislated, unlike the tashahhud. Instead, he proceeds and performs the prostration for forgetfulness (sujud al-sahw) for having omitted it, by analogy to omitting the tashahhud. The second scenario: He stood up from the first prostration and did not sit for the separation (jalsat al-fasl) between the two prostrations. This person has omitted two pillars: the sitting of separation and the second prostration. This is subject to two possibilities: First, that he remembers before beginning the recitation, in which case he is obligated to return. This is the opinion of Malik and al-Shafi'i, and I know of no one who disagrees with it. When he returns, he sits the sitting of separation, then performs the second prostration, and then stands up for the other rak'ah. Some companions of al-Shafi'i said: He does not need to sit because the separation has been achieved by the standing. This is incorrect, because the sitting is mandatory, and standing cannot substitute for it, just as if he had done so intentionally. As for if he had sat for the separation and then stood up without prostrating, he should perform the prostration, and sitting is not required of him. It has been said: It is required of him, so that he may perform the prostration from a sitting position. This is not valid, because he has already performed the sitting, so it is not invalidated by a lapse of forgetfulness thereafter, just like the first prostration, and it becomes as if he had prostrated immediately following the sitting. If he thinks that he had performed two prostrations and sat for the sitting of rest (jalsat al-istirahah), it does not suffice him for the sitting of separation, because it is a posture, and it cannot substitute for a mandatory act, just as if he omitted a prostration from a rak'ah and then prostrated for recitation. The ruling is the same regarding the omission of a pillar other than prostration, such as bowing or the straightening (i'tidal) (42) from it; he should return to it whenever he remembers before beginning the recitation of the next rak'ah, perform it, and then perform what follows it, because what he performed after it is not considered valid due to the loss of the correct order.