Ar-Ra'd - 13:17

أَنزَلَ مِنَ السَّمَاء مَاء فَسَالَتْ أَوْدِيَةٌ بِقَدَرِهَا فَاحْتَمَلَ السَّيْلُ زَبَدًا رَّابِيًا وَمِمَّا يُوقِدُونَ عَلَيْهِ فِي النَّارِ ابْتِغَاء حِلْيَةٍ أَوْ مَتَاعٍ زَبَدٌ مِّثْلُهُ كَذَلِكَ يَضْرِبُ اللّهُ الْحَقَّ وَالْبَاطِلَ فَأَمَّا الزَّبَدُ فَيَذْهَبُ جُفَاء وَأَمَّا مَا يَنفَعُ النَّاسَ فَيَمْكُثُ فِي الأَرْضِ كَذَلِكَ يَضْرِبُ اللّهُ الأَمْثَالَ
[13:17]
He sends down water from the cloud, then watercourses flow (with water) according to their measure, and the torrent bears along the swelling foam, and from what they melt in the fire for the sake of making ornaments or apparatus arises a scum like it; thus does Allah compare truth and falsehood; then as for the scum, it passes away as a worthless thing; and as for that which profits the people, it tarries in the earth; thus does Allah set forth parables.
He sends down water from the skies, and the channels flow, each according to its measure: But the torrent bears away to foam that mounts up to the surface. Even so, from that (ore) which they heat in the fire, to make ornaments or utensils therewith, there is a scum likewise. Thus doth Allah (by parables) show forth Truth and Vanity. For the scum disappears like forth cast out; while that which is for the good of mankind remains on the earth. Thus doth Allah set forth parables.
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.