What should a worshiper do if he discovers his sock is dirty during prayer?

The dirt on a sock does not affect the validity of prayer, and it is not permissible to interrupt the prayer because of it, unless the dirt is an impurity (najāsa). In that case, it must be removed if possible. Otherwise, the prayer should be interrupted and restarted after the impurity is removed. If the dirt is a thick barrier that prevents water from reaching the area required for wiping (masḥ), then wiping over the khuff (leather sock) is not valid. However, if the barrier is not in the area of the obligatory wiping, its presence does not matter unless it is impure.