One who was traveling as darkness approached, and he knew [of] a tree or a fence, and said, ‘‘My Sabbath dwelling place is beneath it,’’ has said nothing. [If, however, he said,] ‘‘My Sabbath dwelling place is at its trunk,’’ he may walk from his present location to the trunk two thousand cubits, and from the trunk to his house two thousand cubits. Thus, he may go four thousand cubits after dark.