Mistake in Sajda Sahw
Sometimes when I am in sajda sahw (second sajda), I doubt if I have sat in jalsa (between prostrations) long enough. So I sit in jalsa again, do sajda again for a third time and say my Salam. Does adding the third sajda invalidate my prayer? Should I repeat it?
Assalāmuʿalaykum Wa Raḥmatullāhi Wa Barakātuh
In the enquired scenario, those prayers that have passed, have passed. In Shā Allāh, Allāh will accept them and there is no need to repeat them.
However, if this occurs in the future, then such prayers should be repeated.
We also advise that you adopt the necessary means to work towards not putting yourself in such a position i.e., to increase concentration and focus on the duration of sitting between any two Sajdahs in that they are at least the duration it takes to recite Subhānallāh once in an average manner.