What does Sajdat al-Sahw mean?
Sajdat al-Sahw is an extra two prostrations (sajdah) to make up for forgetfulness or a mis-take, which is "sahw" in Arabic. While praying, if one makes a mistake that does not nullify the prayer by forgetting somegthing or expe-riencing confusion about something, one has to perform a Sajdat al-Sahw. By so doing, one mends the incomplete acts of a prayer.
In which situations does one have to per form Sajdat al-Sahw?
1. The prostration of forgetfulness (Sajdat al-Sahw) is necessary when there is delay of an obligatory act (fardh) within the prayer. (When we omit one of the obligatory acts (fardhs) of a prayer, such as bowing (al-ruku), our prayer gets nullified. We have to perform it again).
2. The prostration of forgetfulness is necessary when we forget, omit or delay a required act (wajib).
Some situations where we have to make a prostration of forgetfulness (Sajdat al-Sahw)
One cannot sit at the end of the third rakah of a four-rakah prayer. If one sits at the end of the third rakah and recites the supplication of "At-tahiyyatu," then stands up after remember-ing, one has to perform a prostration of for-getfulness (Sajdat al-Sahw) at the end of the prayer. That is because in this situation one has delayed the obligatory act (fardh) of standing (al-qiyam).
When one recites the additional chapter be-fore the Surah al-Fatiha, one has to perform a prostration of forgetfulness (Sajdat al-Sahw). That is because reciting Surah al-Fatiha before the additional chapter is a required act (wajib).
If one goes to bowing (al-ruku) right after reciting Surah al-Fatiha without reciting an ad-ditional chapter, one does not stand up and recite an additional chapter. One continues the prayer with bowing (al-ruku) and prostra-tion (al-sajdah) and performs a prostration of forgetfulness (Sajdat al-Sahw) at the end of the prayer. That is because reciting an additional chapter after Surah al-Fatiha is a required act (wajib) (but not obligatory, i.e., fardh).
While performing the Odd-Numbered Prayer (Salat al-Witr), if one bows (al-ruku), forgetting to recite the Supplication of Qunut (Dua al-Qunut), one does not stand up and recite the Supplica-tion of Qunut. One continues with the prayer and performs a prostration of forgetfulness (Sajdat al-Sahw) at the end of the prayer. That is because reciting the Supplication of Qunut (Dua al-Qunut) is a required act (wajib) but not obligatory (fardh).
If one forgets to sit and stands up after com-pleting the second rakah of a three or four-rakah prayer, one does not sit back down. One continues to pray the third rakah. Then one per-forms a prostration of forgetfulness (Sajdat al-Sahw) at the end of the prayer. That is because both the first sitting and also the recitation of "At-tahiyyatu" are required acts (wajibs) (but not obligatory, i.e., fardh).
If we do more than one mistake in a prayer, how many prostrations of forgetfulness do we have to perform?
For all of the mistakes that require a prostration of forgetfulness, a single prostration would be enough.
How do we perform a prostration of forgetfulness (Sajdat al-Sahw)?
At the final sitting of a prayer, after recit-ing the supplication of "At-tahiyyatu," one gives As-Salam first to the right and then to the left side. Right after that, one goes to prostration (al-Sajdah) by saying "Allahu Akbar" and pros-trating twice. One performs the final sitting one more time and gives As-Salam.