AND [as for] the believers, both men and women they are close unto one another: they [all] enjoin the doing of what is right and forbid the doing of what is wrong, and are constant in prayer, and render the purifying dues, and pay heed unto God and His Apostle. It is they upon whom God will bestow His grace: verily, God is almighty, wise!

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."