What is the ruling concerning rising from the final Tashahhud to an extra rak'ah?
Chapter on the Two Prostrations of Forgetfulness
Al-Mughni
Book of Prayer
Primary text
If one rises from the final Tashahhud to an extra rak'ah, one must return to the final Tashahhud whenever it is remembered, as one has proceeded to an addition that is not validly accounted for, making return obligatory, analogous to remembering before prostration.
Supporting text
The details of this situation will be elaborated upon in the context of praying five rak'ahs. In all three situations discussed (moving when required to return, returning when required to move, and rising to an extra rak'ah), prostration of forgetfulness (Sujud as-Sahw) is required before the concluding salutations (Taslim).