For example...

For example, if one doubts inSalat-ul-ayat, whether he has performed 1 Rak'ah or 2, hisSalat will be void, because it is a doubt which has occurred in aSalat consisting of 2 Rak'ahs. Similarly, if he has a strong feeling that is his first or his second Rak'ah, he will complete the prayer based on that feeling. Sajdat-us-Sahv (Sajdah for Forgotten Acts) Two Sajdat-us-Sahv become necessary in two cases, and they are performed after Salam. Their method will be explained later.

(i) Forgotting Tashahhud. (ii) When there is a doubt in a 4 Rak'ah prayer, after entering second Sajdah, as to whether the number of Rak'ahs performed is 4 or 5, or 4 or 6 like the fourth case in valid doubts. And in three cases, Sajdat-us-Sahv is, as an obligatory precaution, necessary: (i) For talking forgetfully during prayer. (ii) Reciting Salam at the wrong place, like, forgetfully reciting it in the first Rak'ah.

(iii) When after y'Salatt, one realises that he has either omitted or added something by misatke, but that omission or addition does not render tha prayer void. If a person talks, by mistake or under the impression that his prayer has ended, he should perform 2 Sajdat-us-Sahv, as a precaution.

If at a time where the Salam of prayer is not to be said, a person forgetfully says As-salamu alayna wa ala ibadi-llah-is-salihin or says: As-salamu alaykum, he should, as an obligatory precaution, perform 2 Sajdat-us-Sahv, even if he did not add “Wa rahmatu-llahi wa barakatuh”. But if he says: “As-salamu alayka ayyuhan-nabiyyu wa rahmatu-llahi wa barakatuh”, then Sajdat-us-Sahv will be a recommended precaution.

If one utterstwo or more letters of Salam, he should, as an obligatory precaution, offer two Sajdat-us-Sahv. If a person says, by misatke, all the 3 Salams at the time when Salam should not be recited, it is sufficient to perform 2 Sajdat-us-Sahv. If a person remembers during Ruku or thereafter, that he has forgotten one Sajdah or Tashahhud of the preceding Rak'ah, he should perform the Qada of Sjadah after the Salam of prayer, nad for Tashahhud he should perform two Sajdat-us-Sahv.

If a person does not perform Sajdat-us-Sahv after the Salam of prayer intentionally, he commits a sin, and it is obligatory, as a precaution, upon him to perform it as early as possible. And if he forgets to perform it, he should perform it immediately when he remembers.