And God's is the east and the west: and wherever you turn, there is God's countenance. Behold, God is infinite, all-knowing.
Al-Baqara (The Cow) Verse 115
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