The Originator is He of the heavens and the earth: and when He wills a thing to be, He but says unto it, "Be" -and it is.
Al-Baqra (The Cow) Verse 117
Allah's Apostle said, "Don't sell gold for gold unless equal in weight, nor silver for silver unless equal in weight, but you could sell gold for silver or silver for gold as you like."
Sahih Bukhari: Volume 3, Book 34, Number 383