"When they reached the junction between them, they forgot their fish, and it took its way"—meaning the fish—"into the sea, as a tunnel [saraban]."

Muhammad said: Saraban means a path or a course. It is a verbal noun [masdar]. The meaning is: they forgot their fish, and the fish made its path in the sea. Then He explained how that happened, as if He said: saraba yasrubu saraban (it flowed/channeled, it flows, a flow/tunneling).