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 sent down water from the heavens, so the canals flowed according to their capacity, and the flood carried bulging scum. And a similar scum comes up from what they melt in the fire to obtain ornaments or other objects. This is how Allah depicts the truth and the untruth. As for the scum, it goes to be thrown away, while that which benefits people remains on the earth. This is how Allah brings out the parables.