Sujood al-Sahw: The Prostration of Forgetfulness

It addresses three kinds of lapse: adding something by mistake (an extra bow or unit), omitting a required but non-essential part (such as the first sitting), and doubting how much you have prayed. It does not fix a missing pillar such as a prostration — that part must actually be performed.

It is simply two prostrations like those in the prayer, made near the end. The schools differ on timing: some perform both prostrations before the closing salam, others after it, and some vary by the type of mistake. Each practice is transmitted and accepted.

When unsure whether you prayed, say, three units or four, the common guidance is to build on what you are certain of (the smaller number), complete the prayer, and then make the two prostrations. This removes the need to restart over every passing doubt.

Sujood al-Sahw exists so that forgetfulness — a natural part of being human — never spoils an honest prayer. For lapses serious enough to actually break the prayer, see what invalidates the prayer.