Sajda Sahv means genuflection of mistake and is for indemnity of a non-intentional mistake in prayer.
According to Fiqh of Shia Islam Sajda Sahv is for doing a mistake in obligatory prayers.
If any of the following five types of mistakes occurs forgetfully
during a wajib salat, then it is wajib to perform Sajdah Sahv
immediately after completing the salat.
(1) Talking forgetfully during
salat (or even uttering a single word which has a meaning, e.g. saying
‘Ah’ in pain).
(2) Reciting Salam forgetfully at a wrong place during salat. (For
example, if you recite Salam after Tashahhud in 2nd rakat in a 4-rakat
salat). Salam in a salat has three parts. Sajdah Sahv becomes wajib if
2nd or 3rd part of Salam is recited forgetfully. If only 1st part is
recited forgetfully, then Sajdah Sahv is not wajib, but it is mustahab
(3) Forgetting to recite Tashahhud during salat. If you forget
Tashahhud after 2nd rakat, but remember it before the ruku of next
rakat, then you should return and perform it. And after the salat,
perform Sajdah Sahv for performing additional standing (qiyam).
(4) Adding or omitting something forgetfully during salat, but that
addition or omission does not make salat void. (Examples: (i)
reciting Tashahhud after 1st rakat or after 3rd rakat in a 4-rakat
salat; (ii) doing an extra sajda by mistake; (iii) forgetting zikr
in a sajdah or ruku, (iv) forgetting second surah in 1st rakat or 2nd
(5) When doubts occurs in the number of rakats in a 4-rakat salat, if
it is 4th or 5th rakat, or it is 4th or 6th rakat, or it is 4th or
more rakat (as explained in Fiqh Notes #2).
Lecture #3 Maulana Abul Qasim Rizvi, Panjtan Ctr, Melb rev 160107 5
SAJDAH SAHV, NOTES OF LECTURES ON FIQH - By Maulana Abul Qasim Rizvi