If you have been praying for victory, [O believers] - victory has now indeed come unto you. And if you abstain [from sinning], it will be for your own good; but if you revert to it, We shall revoke [Our promise of aid] - and never will your community be of any avail to you, however great its numbers: for, behold, God is [only] with those who believe !
Al-Anfal (The Spoils of War) Verse 19
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