Having doubts regarding one's Salah and forgetting to say 'Subhana Rabiyy al-`Adhim' in Ruku`
If you have doubts concerning your Salah, you should continue praying based on the actions you are sure that you have performed, and then you should perform Sujud-ul-Sahw. If you forget to perform Sujud-ul-Sahw and there is a long intervening period, then nothing is required of you. Saying "Subhana Rabbiyal-‘Adhim" is obligatory in Ruku‘ (bowing), but if you forget it then you should perform Sujud-ul-Sahw and your Salah will be correct.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.