All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallahu ‘alayhi wa sallam, is His slave and Messenger.
In his commentary on the Fiqh book Al-Muqni’, the Hanbali scholar Ibn Muflih said:
“...When he performs Sujood as-Sahw after Tasleem, regardless of whether he was supposed to perform it after Tasleem or before it but he forgot and then performed it after Tasleem, he must recite the final Tashahhud as an obligation. This is the view of a group of scholars including Ibn Mas‘ood, as evidenced by the hadeeth narrated on the authority of ‘Imraan, who reported that the Prophet, sallallahu ‘alayhi wa sallam, forgot (something), so he performed two prostrations and then recited the Tashahhud and then made Tasleem... [Abu Dawood; At-Tirmithi - At-Tirmithi graded it hasan (good)] Moreover, he should recite the Tashahhud (after Sujood as-Sahw) because it is a prostration that requires Tasleem, so it has to be followed by the Tashahhud and then Tasleem, just like the obligatory, final Tashahhud of the prayer ... Another view holds that one should not recite Tashahhud in this case, just like the Sujood as-Sahw before Tasleem, and this view was chosen by Shaykh Taqiyy Ad-Deen (Ibn Taymiyyah).” [Sharh Al-Muqni’]
Allah knows best.