When must the Imam perform the prostrations of forgetfulness (Sujud as-Sahw)?
Chapter on the Two Prostrations of Forgetfulness
Al-Mughni
Book of Prayer
Primary text
The general rule is that all prostrations for forgetfulness (Sujud as-Sahw) are performed before the final salam (Taslim), according to Ahmad. This applies to cases where one doubts the number of units prayed, stands where one should sit, sits where one should stand, recites silently where one should recite aloud, recites aloud where one should be silent, prays five units, or any other similar error of forgetfulness. This is because it pertains to the prayer itself, thus it should be rectified before concluding the prayer. Only two specific situations mandate prostration after the salam: when the Imam concludes prayer due to an omission ( نقص), as in the Hadith of Dhu al-Yadayn, or when the Imam builds his prayer upon his dominant guess (taharri) after a doubt, as narrated in the Hadith of Ibn Mas'ud.
Supporting text
There is a difference of opinion regarding the case where the Imam prays five units; one narration suggests before salam, and another suggests after salam. Al-Shafi'i holds that all prostrations should be before the salam, citing the Hadith of Ibn Buhaynah and Abu Sa'id, arguing that it is a completion and compensation for deficiency, thus preceding the salam like other parts of the prayer. Another view, held by Malik and Abu Thawr, dictates that prostrations for deficiency should be before the salam (per Ibn Buhaynah), while prostrations for addition should be after the salam (per Dhu al-Yadayn and Ibn Mas'ud's case of praying five). The opinion of the People of Reason (Ahl ar-Ra'y) is that all prostrations for forgetfulness occur after the salam, citing the Hadith of Thawban and Ibn Ja'far.