HAD WE bestowed this Qur’an from on high upon a mountain, thou wouldst indeed see it humbling itself, breaking asunder for awe of God.   And [all] such parables We propound unto men, so that they might [learn to] think.

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."