He sends down out of heaven water, and the wadis flow each in its measure, and the torrent carries a swelling scum; and out of that over which they kindle fire, being desirous of ornament or ware, out of that rises a scum the like of it. So God strikes both the true and the false. As for the scum, it vanishes as jetsam, and what profits men abides in the earth. Even so God strikes His similitudes.