How & when to perform sûjûd al-sahw

Question

What should a person do when he makes a mistake in prayer like leaving out something essential or doing something too many times?

Answer

The prostration of forgetfulness (sûjûd al-sahw) is exactly like the prostration that is performed during prayer. You say the same supplications, like: "Subhâna Rabbî al-A`lâ" and: "Subhânaka Allhumma wa bihamdika. Allahuma-ghfir lî." 

Sûjûd al-sahw is performed for three reasons:

(1) when the worshipper performs something additional 

(2) when the worshipper leaves something out 

(3) when the worshipper suspects adding something or leaving something out

An addition in prayer could be something like inadvertently performing an extra unit of prayer, or an extra bow, or an extra sujûd. 

Leaving something out could be something like forgetting to perform the tashahhud, or forgetting the tasbîh in the sûjûd or something like that. 

A suspicion is where the worshipper is unsure as to what he has done; for instance, he may be unsure as to whether he has prayed three or four units. 

In case the worshipper believes or is certain that he might have done too much or too little, he should act according to what he believes is right and then perform sûjûd al-sahw after thesalâm. 

In case he is unsure one way or the other, he should perform what he suspects he might have left out and then perform sûjûd al-sahw before the salâm. 

Some scholars are of the opinion that sûjûd al-sahw should always be performed before thesalâm. 

And Allah knows best.

-islamtoday.net