When is the reward for congregational prayer counted? Should a worshiper interrupt his prayer and join another congregation if he catches the Imam in the final tashahhud? And what is the ruling on passing in front of a worshiper?

It is more likely that a line can be considered a substitute for a sutra when one is unavailable, which is the view of some scholars, such as Imam Ahmad. He holds that the end of the prayer rug on which the worshipper prays can serve the purpose of a line if a sutra is not available, because it carries the same meaning, similar to a stick laid horizontally in front of the worshipper when unable to erect it. Indeed, Imam Ahmad permitted placing a stick horizontally in front of the worshipper.