he sends down water from the sky and the valleys flow according to their measure but the flood bears away the foam that mounts up to the surface and from that which they heat in the fire in order to make ornaments or utensils rises a foam like unto it thus does allah show forth truth and falsehood. then as for the foam it passes away as scum upon the banks while that which is for the good of mankind remains in the earth. thus allah sets forth parables .
أنزل من السماء ماء فسالت أودية بقدرها فاحتمل السيل زبدا رابيا ومما يوقدون عليه في النار ابتغاء حلية أو متاع زبد مثله كذلك يضرب الله الحق والباطل فأما الزبد فيذهب جفاء وأما ما ينفع الناس فيمكث في الأرض كذلك يضرب الله الأمثال