Verse 17 of Chapter 13:

 

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 (also) from that (ore) which they heat in the fire in order to make ornaments or utensils, rises a foam like unto it, thus does Allah (by parables) 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.

Verses 1-4 of Chapter 13:

Alif. Lam. Mim. Ra. These are the verses of the Divine Book, and that which has been sent down to you from your Lord is the very truth, but most (of your) people do not believe in this. It is Allah Who raised up the heavens without such pillars as you could see: then He sat Himself upon the Throne of His Kingdom: He subjected the sun and the moon to a law. Everything in the universe is running its course to its fixed term. And Allah alone is directing the whole affair. He makes His signs plain: perhaps you may be convinced of meeting your Lord. And it is He Who has spread out the earth, and fixed the immovable mountains in it, and made the rivers flow on it. He has created in pairs every kind of fruit, and He covers the day with the veil of night. Surely there are great Signs in these for those who reflect upon them. And behold! there are different regions on the earth close to one another; there are vineyards, corn fields and groves of date-palm with single or double trunk. All are irrigated with the same water, but We make some more tasteful than others. Most surely there are many Signs in all these things for those who use their common sense.