He sends down water from the sky and the valleys flow (in abundance) each according to its measure, and the flood carries a swelling foam (on its surface). And out of what they smelt in the fire in order to make ornaments or utensils, there rises a scum like it. Thus does God strike a parable to illustrate truth and falsehood. For, as for the scum, it vanishes as does all dross, but that which is of use to people abides on earth. In this way does God strike parables.