AND MUHAMMAD is only an apostle; all the [other] apostles have passed away before him: if, then, he dies or is slain, will you turn about on your heels? But he that turns about on his heels can in no wise harm God - whereas God will requite all who are grateful [to Him].

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."