Is the prostration of forgetfulness (sujud ba'di) obligatory upon a traveler if he prays 'Isha and stands for the third rak'ah, then completes it?

If a traveler performs the Isha prayer and shortens it, then forgets and stands for the third unit (rak'ah) and completes it, he must perform the prostration of forgetfulness (sujud al-sahw) before the salutation (taslim) due to the addition in the prayer. However, if he deliberately stands for the third unit and continues with it without a valid reason requiring completion (such as intending to reside), then his prayer is invalidated. If he stands for the third unit out of forgetfulness and then remembers, he must return to the tashahhud and perform the prostration of forgetfulness.