Q: What is the ruling on Sujud-ul-Sahw (Prostration of Forgetfulness)? What should be said during it? When should it be before taslim (salutation of peace ending the Prayer), and when after Taslim? When it is after Taslim, should Taslim be on the right side only, or on both the right and left sides?
A: Sujud-ul-Sahw is Wajib (obligatory) when the worshipper absentmindedly does not perform a Wajib act of Salah or performs a prohibited act therein because Allah’s Messenger (peace be upon him) ordained the same and did it himself.He (peace be upon him) said: ”Offer Salah as you have seen me offering Salah. ”The worshipper offering Sujud-ul-Sahw says what is usually said during the regular Sujud: ’Subhana Rabbiya Al-A’la (Glory be to my Lord, the Most High) twice , ’Subhanaka allahuma rabbana wa-bihamdika (Glory be to You our Lord and all Praise be to You), and ‘Allahum-maghfir li (O Allah, forgive me). Then, the worshipper should supplicate Allah (Exalted be He). Sujud-ul-Sahw is permissible before and after Taslim, but it is preferable to be offered before Taslim except in two cases:
When the worshipper makes Taslim while they have not performed one Rak’ah (unit of Prayer) or more, in which case they should offer Sujud-ul-Sahw after Taslim [after making up for the missed Rak’ah] because Allah’s Messenger (peace be upon him) offered Sujud-ul-Sahw after Taslim when he absentmindedly forgot to perform one Rak’ah or two in another narration. Taslim after Sujud-ul-Sahw is made on both the right and left sides.
Likewise, the worshipper should offer Sujud-ul-Sahw after Taslim when they side with a certain thought in preponderance over the other regarding how many Rak’ahs they have performed. If, for example, the worshipper mostly thinks they have performed three or four Rak’ahs and accordingly completed their Salah, they should offer Sujud-ul-Sahw after Taslim. In all instances of Sujud-ul-Sahw, the worshipper should make Taslim from it on both the right and left sides. This is what the Prophet (peace be upon him) used to do.
Source: Fatwas of Nur ‘Ala Al-Darb, Question no. 170, Volume.9, Part No.9; Page No. 378-379 | www.alifta.net