Ruling on selling nine riyals of halalah for ten paper riyals?

Question:
This is a question that has been asked frequently. It concerns exchanging the coin currency, halalah, for paper riyals: giving ten paper riyals for nine riyals of halalah. Is this permissible?

Answer:
Many of our brothers among the scholars have issued a ruling that it is permissible, while some of our brothers have issued a ruling that it is prohibited. It is a matter of doubt. Those who ruled it permissible said that it is an independent currency; the metal is not the paper, so the difference in value is permissible, like gold and silver exchanged hand-to-hand, and there is no difference in quantity. And what is the protection? He said that it is one riyal that prevents an increase. So it is like asking someone to leave that off, out of caution, based on the saying: "Leave what causes doubt for what does not cause doubt." One should not sell to anyone a riyal except for an equal amount hand-to-hand, because everything called a riyal falls under the category of precaution. Yes.