If a person says recommended dhikr while moving – for example, he says takbīr while going into rukūʿ or sajdah – in the event that he says it with the intention of it being a dhikr that has been prescribed in prayers, that dhikr is not valid but his prayer is valid.
The [recommended] sentence: بِحَوْلِ اللهِ وَقُوَّتِهِ أَقُوْمُ وَأَقْعُدُ biḥawlil lāhi wa qūwwatihi aqūmu wa aqʿud By Allah’s power and His strength I stand and sit....should be said while getting up [after the completion of a rakʿah].