Q.1) What is compensatory prostration? How and when should it be done?
Ans) Performing 2 prostrations after Tashahud of the last sitting because of the occurrence of an error in the prayer is called Compensatory Prostration.

The method of performing compensatory prostration is, in the last sitting after Tashahud one has to convey one salam towards the right shoulder and then perform two prostrations thereafter repeat the tashahud with Durud and Dua (supplication). Then convey salam on both sides.

It becomes obligatory due to the below five reasons:

1. Advance performance of any posture (i.e., before Qirat, doing Ruku or Sajda).
2. Delay in performance of any posture (Ex: Reciting more than the tashahud in the first sitting due to which there is delay in standing for the third Rakaat).
3. Repetition of any posture (Ex: Performing 2 Ruku or 3 Sajdas) in any Rakaat.
4. Dropping of any Obligation (Ex: First sitting is avoided).
5. Change in Obligation (Ex: Reciting Quran loudly when it is to be read slowly).

Q.2) Give few examples of Sajda Sahu.
Ans) Below are the examples of Sajda Sahu:

1. If by mistake any of the posture or condition of namaaz is left out then prayer should be repeated again. Even compensatory prostration cannot complete the Namaaz.
2. If forgotten to recite Surah Fateha or only combined Surah is recited or initially combined Surah then Surah Fateha is recited then compensatory prostration becomes obligatory.
3. It is obligatory to recite combined Surah in all the Rakaats of Sunaat, Nafil and Vitar. If someone recites combined Surah only in the first two Rakaats similar to Farz Namaaz and leaves the combined Surah for the rest two Rakaats then Compensatory Prostration becomes obligatory.
4. After reciting Surah Fateha and for combined Surah, if there is a delay such that one posture can be performed in that delay (or) in the first sitting after tashahud if there is a delay in standing such that one posture can be performed in that delay then compensatory prostration becomes obligatory.
5. In first sitting(Qaida-e-Oola) of 3 or 4 Rakaats prayer after Tashahud, instead of standing if someone starts reciting Durud Ibrahim and have uttered till ‘Allah-hum-ma Sal-le-Ala’ and stood for third Rakaat then compensatory prostration is not obligatory but if uttered more than this then it becomes obligatory.
6. In 3 or 4 Rakaats prayer, after 2 Rakaats if forgotten to sit and stood up completely and recollected to sit then do not sit back otherwise prayer will be nullified because one should not return from Farz to Wajib. And if recollected while standing such that the position is near to sitting then sit down for Tashahud and do not perform compensatory prostration. And if the position is near to standing then do not sit and perform compensatory prostration.