One Who Forgets The Tashah-hud While He Is Sitting Sunan Abi Dawud 1036
Translation
Narrated Al-Mughirah ibn Shu'bah
When the imam stands up after the two rak'ahs, if he remembers before standing straight up, let him sit down; but if he stands straight up, let him not sit down, and let him perform the two prostrations of forgetfulness.
Abu Dawud said: And there is not in my book any hadith from Jabir Al-Ju'fi except this one.