He sends down water from the sky whereat the valleys are flooded to [the extent of] their capacity, and the flood carries along a swelling scum. And from what they smelt in the fire for the purpose of [making] ornaments or wares, [there arises] a similar scum. That is how Allah compares the truth and falsehood. As for the scum, it leaves as dross, and that which profits the people remains in the earth. That is how Allah draws comparisons.