السلام عليكم ورحمة الله وبركاته احسن الله اليك The dua: Subhana kalla humma wabihamdika wa tabarakasmuka --- (and so on), is this Du'a also mandatory to recite when praying behind an imaam? Sometimes they don't leave enough time for us to read it before starting with Al Fatihah.

Ustadh AbdulAziz al-Haqqan

This is a sunnah akhi not mandatory in any case