Examples

He sends down water from the sky, and valleys flow according to their measure. The torrent carries foam like the scum upon molten metal when heated for crafting ornaments or tools. Thus, Allah illustrates truth and falsehood, the foam vanishes, but what benefits people remains. This is how Allah sets forth examples.

13:17He sendeth down water from the sky, so that valleys flow according to their measure, and the flood beareth (on its surface) swelling foam - from that which they smelt in the fire in order to make ornaments and tools riseth a foam like unto it - thus Allah coineth (the similitude of) the true and the false. Then, as for the foam, it passeth away as scum upon the banks, while, as for that which is of use to mankind, it remaineth in the earth. Thus Allah coineth the similitudes.