Is Sujud As-Sahw (prostration of forgetfulness) obligatory upon us due to the Imam standing for a fifth rak'ah, then returning to the Tashahhud and making the Tasleem without performing Sujud As-Sahw?

If a worshiper stands up for an extra unit of prayer (rak'ah) and remembers before fully rising from the sitting position, there is no prostration of forgetfulness (sujud al-sahw) required. However, if he has fully risen from the sitting position, then sujud al-sahw is required. If the Imam makes a mistake in prayer and sujud al-sahw is due but he does not perform it, the congregant (ma'mum) follows him in the taslim (salutation of peace). The majority of scholars hold that the congregant should perform sujud al-sahw after the Imam's taslim to rectify the error, unless the Imam himself does not believe in the obligation of sujud al-sahw in the first place; in that case, the congregant is not required to prostrate.