Is Tawarruk performed in the Tashahhud of the prostration of forgetfulness (Sujud as-Sahw)?
Chapter on the Description of Prayer
Al-Mughni
Book of Prayer
Primary text
If the prostration of forgetfulness occurs after a second Tashahhud in a four-rak'ah prayer, Tawarruk is performed in that Tashahhud because it is considered part of the original prayer's final Tashahhud. Similarly, if the prostration of forgetfulness occurs after the final Salam, Tawarruk is performed because it functions as a second Tashahhud in the prayer, requiring differentiation from the main Tashahhud of the prayer itself.
Supporting text
Regarding a person joining a four-rak'ah prayer late and catching only the last rak'ah with the Imam: if the Imam sits for the final Tashahhud, the latecomer has the option (*in sha'a*) to perform Tawarruk with the Imam. When the latecomer stands to complete his missed rak'ah, he should perform Tawarruk in his final Tashahhud because it is the fourth rak'ah for him.