What is the ruling on exchanging ten paper riyals for nine metal riyals?

The questioner : All right, a second issue as well, regarding the exchange of money. For example, using the telephone requires coinage, so you give a specific person ten riyals and he gives you nine riyals; ten paper riyals and he gives you nine riyals. Is the one who issued the fatwa for Shaykh Ibn Uthaymeen saying that this is permissible because the two types differ? Paper is one thing and metal is another?

The Shaykh : ... the difference is that paper has no intrinsic value, whereas metal may have more value than paper. This is said regarding coins and silver; silver is not gold, and silver is not coins. This is said. But paper currency is neither silver nor gold; it is paper currency that has no value except for the estimated gold value assigned to it.
The student : He, the Shaykh, says that this has become a commodity like the commodities found in the market.
Another student: Our Shaykh, you say that this is riba, yes?

The Shaykh: Yes.