Assalaamu alaykum. I have just concluded the Maghrib prayer behind the imam (I was following behind the imam) when I got up from bowing and realized (or at least predominantly believe) that I forgot to do tasbeeh (saying 'sobhaan Allaah') even once. At the time, I was distracted with errant thoughts and did not realize until I was in the middle of the transition (or perhaps even after) that I had forgotten to say it even once. I know that it is an obligatory part of the prayer, but I do not know what to do now that I know/predominantly believe that I forgot it.

All perfect praise be to Allaah, The Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad is His slave and Messenger.

Reciting tasbeeh in rukooʻ (bowing) and sujood (prostration), either once or more, is an act of Sunnah and is not obligatory according to the view of the majority of scholars. When the person intentionally or unintentionally misses reciting the tasbeeh in rukooʻ or sujood, his prayer is still valid and he is not required to repeat it.

It seems that the dear questioner might be suffering from waswaas (obsessive whisperings), as has reflected in his past questions; so there is no harm in him following the scholarly view of the majority of scholars in this regard, and he is not liable for anything, and his prayer is valid. We hope that Allaah would bless him with total recovery from such obsessive whisperings.

Allaah knows best.