Forgetfulness in Prayer

All Praise is for Allah, the Lord of all creation, and may He extol and send blessings of peace upon our Prophet Muhammad who delivered the clear message, and upon his true followers, his Companions, and those who follow them upon good until the Day of Requital. To proceed:

Then many people are ignorant about many of the rulings concerning the Sujoodus-Sahw (prostration for forgetfulness) in the prayer. Some of them leave the Sujoodus-Sahw when it is obligatory upon them; others perform the prostration in other than its correct place; some perform it before the salaam (salutation at the end of the prayer) even in cases when’ it has to be performed after the salaam; others prostrate after the salaam even when it should be performed before it. Therefore, it is very important to become aware of its rulings, especially for the Imams whom the people follow in their prayers, and who have therefore taken on the responsibility of following that, which is correct and prescribed in their prayers, and of leading the Muslims upon that.  So  I  wished  to  put  before  my brothers some of the  rulings in this regard, hoping that Allah, the Most High, will cause it to be of benefit to His believing servants.

So I say, whilst seeking the help of Allah, the Most High, and asking Him to guide us to and grant us what is correct:

The Prostration of Forgetfulness is: two prostrations that the one praying makes in order to compensate for mistakes occurring in the prayer due to forgetfulness (sahw).

Its  causes  are  three:  having  added  something  (az- Ziyaadah),  having  omitted  something  (an-Naqs)  and having been in a state of doubt (ash-Shakk).