What should the worshipper and the imam do if the imam says "Allahu Akbar" instead of "Sami'a Allahu liman hamidah" when rising from bowing in the Maghrib prayer?

If the Imam forgets an obligatory act of prayer, such as saying "Sami' Allahu liman hamidah" (Allah hears those who praise Him) after rising from Ruku' (bowing), and does not remember it until it is too late, he must perform two prostrations of forgetfulness (Sajdat al-Sahw) before the Taslim (salutation). It is incumbent upon the congregant (Ma'mum) to alert him. If the Imam does not pay attention, the congregant should perform his own obligation, which is to say "Rabbana wa lakal-hamd" (Our Lord, and to You be all praise). If the Imam remembers his obligation in time, then nothing is required of him.