He sends down water from the skies, and the channels flow, each according to its measure: But the torrent bears away to foam that mounts up to the surface. Even so, from that (ore) which they heat in the fire, to make ornaments or utensils therewith, there is a scum likewise. Thus doth God (by parables) show forth Truth and Vanity. For the scum disappears like forth cast out; while that which is for the good of mankind remains on the earth. Thus doth God set forth parables. (13:17)