Must a worshiper return to prostrate himself before sitting for the Tashahhud if he rises from the second prostration, intending to stand, and then remembers that he has added a Rak'ah or forgotten the first Tashahhud?

If someone stands up for an extra rak'ah inadvertently, or inadvertently stands up from the first tashahhud but has not fully straightened up, they should immediately return to the sitting position and do not need to prostrate again. Ibn Qudamah said: "If he remembers while he is in the extra rak'ah, he should sit down immediately." However, if someone rises from rukū' (bowing) or bends into rukū' upon hearing a startling sound, for example, and did not intend to move from the pillar of the prayer, then they must return to that pillar to complete their prayer.