Prostration of forgetfulness: one of the misconstrued subjects in solah

There are three (3) cases that could warrant sujoodu-s-sahw:
(i)ٱلزيادة(Addition): Eg. forgetfully adds extra standing, bowing (rukuu'), prostration (sujood), sitting, tasleem etc.
(ii)ٱلنقص(Omission): Forgetfully omits required/compulsory aspects (wajibaatul solah). Eg. 1st tashahhud; saying of "sami'aLLahu liman hamidahu/Rabbana laka hamd" while raising from rukuu' etc.
(iii) ٱلشك (Doubt): Eg. Doubting if you are in 2nd or 3rd raka'
For either of the three aforementioned cases would require:
(a) Ba'di'-Two prostrations with tasleem, after the tasleem of the solah; without an additional tashahhud.
(b) Qabli- Two prostrations before the tasleem of the solah. Afterwards, one would make tasleem, without no additional tashahhud.
Cases and applications:
(i) Addition in solah (Aziyaadah) requires ba'di- Eg. (a) forgetfully observed five (5) raka'aat in Zuhr, Asr  or Isha' instead of four (4). In this case, he has unintentionally added a raka', which makes ba'di binding on him as an expiation.
(b). Forgetfully observed two (2) raka'tain in Zuhr, Asr or Isha' prayer instead of four (4). The person would stand to complete the remaining two (2) raka'tain after which ba'di is required. In this case, he has mistakenly added an additional tasleem which is the first tasleem he made mistakenly.
(ii) Omission (An-naqs) in solah requires Qabli- Eg. Forgetfully omits first tashahhud in Zuhr, Asr, Magrib or Isha' prayer. In this case, the person would continue his solah (provided he has stood erect, but if he remembers while he is about to stand up, he should sit to perform his tashahhud with no sujood-s-sahw) and after the last tashahhud, before tasleem, he would prostrate twice (qabli), after which he would make tasleem (no additional tashahhud). 
(iii) Doubt in solah (As-shakk) is subdivided into two:
(a) Doubt with certainty (Shakkul yaqeen) in solah requires ba'di. Eg. one is in doubt if he is in the 2nd or 3rd raka'aat of a Zuhr prayer. But his mind tells him it should be the 3rd raka'aat because it seems he sat for 1st tashahhud. He should make it 3rd raka'aat, add one more raka', perform tashahhud/tasleem and prostrate twice (ba'di) with tasleem afterwards.
(b)Doubt without certainty (shakku gairal yaqeen) in solah requires qabli. Eg. a person is in doubt if he is in the 2nd or 3rd raka'aat of a magrib prayer. And neither of the two is certain in his mind, he should act upon the lesser one. Thus, he makes it 2nd raka' performs tashahhud; add one more raka' and after tashahhud, he prostrate twice (qabli), then say tasleem.
There is no special supplication while in sujuud-s-sahw but we are expected to recite the same supplication of sujuud i.e. سبحان ربى الأعلى  -Subhaana rabiyal 'alaa and there is no need for additional tashahhud.
© Muritala Raji (MR) 
١ صحيح فقه السنة Saheeh fiqhus-sunnah
٢ ٱلوجيز في فقه ٱلسنة وٱلكتآب ٱلعزيز
٣ سجود ٱلسهو by Sheikh Muhammad Ibn 
                        Saalih Al-Uthaimeen
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