What should the Imam do when he stands to offer an additional Rak`ah but hears the Ma'mums' Tasbih?
When the Imam stands up for an extra Rak`ah out of forgetfulness and then he realizes this or is reminded by the Ma'mums (those being led by an Imam in Prayer), he has to return to the sitting position for making Tashahhud (a recitation in the sitting position in the second/ last unit of Prayer). The Imam has then to make Taslim followed by Sujud-ul-Sahw. However, Sujud-ul-Sahw may also be performed before making Taslim.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.