If one is offering prayers (salah) in congregation (Jama'ah) and he commits a mistake under which sajdah for repentence becomes mandatory, then, can he offer such a sajdah at the end of the prayers (salah)? If yes, please specify the correct procedure for the same and clarify the situations under which one must perform such a sajdah while in congregational prayers.
If a person offering his salah with jama'ah commits a mistake behind his Imam which is normally remedied by the sajdah of sahw, he need not, and should not, offer the sajdah of sahw, because the sajdah of sahw is obligatory only on a person praying individually or on a person leading the prayer. As for a person praying behind his Imam as a muqtadi, the rules of sajdah of sahw are not applicable on him. His salah will be valid without the sajdah of sahw, unless he leaves an obligatory (Fard) act altogather, like the sajdah, or ruku' etc. In which case the sajdah of sahw will not be sufficient to correct the error, but his salah will be void and he will have to offer the prayer once again.
As for those mistakes which are remedied by the sajdah of sahw for an Imam or for a person praying individually they are forgiven for a person praying behind the Imam, and his salah is deemed to be complete without the sajdah of sahw.
However, if the person has missed one or two rak'at from the jama'ah and he is offering the missed rak'at on his own after the congregational prayer is over, and he makes a mistake for his duration, he will have to offer the sajdah of sahw, because, while completing the missed raka'at he is deemed to be a person who offers the prayer individually, and the sajdah of sahw is obligatory on him like any other individual.
Fatawa by Mufti Muhammad Taqi Usmani.