What is the ruling on latecomers in congregational prayer moving forward, right, left, or backward to complete the rak'ahs they missed, and is this movement obligatory or sunnah, and what is its extent?

Many believe that it is commendable for a latecomer (masbuq) to move during the completion of their prayer, but this belief has no basis in the Sunnah and was not transmitted from the Prophet (peace be upon him) or his companions. Moving in prayer without a valid reason is considered disliked futility, based on Allah's saying: "Successful indeed are the believers those who are humble in their prayers," and the Prophet's (peace be upon him) saying: "Indeed, there is preoccupation in prayer."

However, there is no harm in slight movement for a valid reason, such as making space for passersby or standing behind a sutrah (barrier). It has been authentically reported that the Prophet (peace be upon him) would turn his head during prayer to attend to a matter, and he advanced and retreated during the eclipse prayer. But if this movement is without a valid reason, it is disliked, and if it is coupled with the belief that it is sunnah, then it falls within the realm of innovation (bid'ah).