Ar-Ra'd 13:17 انزل من السماء ماء فسالت اودية بقدرها فاحتمل السيل زبدا رابيا ومما يوقدون عليه في النار ابتغاء حلية او متاع زبد مثله كذالك يضرب الله الحق والباطل فاما الزبد فيذهب جفاء واما ما ينفع الناس فيمكث في الارض كذالك يضرب الله الامثال ١٧

He 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.