Increase or decrease in Salah

Q 1: I joined the congregation at the beginning of a four-Rak`ah Salah (Prayer consisting of four units) and did not miss any of it. After saying the Taslim (salutation of peace ending the Prayer), I mistakenly offered a fifth Rak`ah, but the person next to me drew my attention to my error. What should I do, should I repeat the Salah or not? What if the time between the two actions was long?

A: Anyone who does that and offers a fifth Rak`ah in error should perform Sujud-ul-Sahw (Prostration of Forgetfulness), but they do not need to repeat the Salah.