The World Federation One Stop Fiqh

Ruling 1016

While performing rukūʿ, the body must be still and one must not intentionally move his body in a manner that it is no longer still, even when – based on obligatory precaution – he is not saying an obligatory dhikr. If a person intentionally does not observe this requirement to be still, then based on obligatory precaution, his prayer is invalid even if he says dhikr while his body is still.