Answered by Shaykh Faraz Rabbani
As an imam, if one forgets to recite ‘sami Allahu liman hamida’ aloud, is sajda sahw binding upon him?
Walaikum assalam,
Saying the dhikrs of the prayer is a confirmed sunna. Forgetfulness prostrations are necessary (wajib) only when a necessary action of the actions of the prayer is omitted forgetfully. [Durr al-Mukhtar]
See: (http://www.SunniPath.com) and Related answers.
Wassalam,
Faraz