What is the ruling on the first Tashahhud in the eighth raka’ah of the nine-raka’ah Witr prayer, and does forgetting it necessitate the prostration of forgetfulness (sujud as-sahw), and is it permissible for the prostration of forgetfulness to be performed after the taslim in this case?

It is permissible to pray Witr with nine rak'ahs, with a single tashahhud at the end, or with two tashahhuds, where one sits for the first at the eighth rak'ah, then performs the tasleem after the ninth. If one intended the middle tashahhud but did not perform it, the prescribed action is to perform the prostration of forgetfulness (sujud al-sahw) at the end of the prayer. Indeed, the Shafi'is and Hanbalis hold that the first tashahhud is compensated for by sujud al-sahw if it is omitted forgetfully or intentionally. If one forgets sujud al-sahw before the tasleem, one performs it after the tasleem.