Is it permissible to exchange paper currency at different rates?

The Shaykh : ... It is not permissible to buy two sa' of inferior dates with one sa' of good dates, or the reverse. Why? Because dates are among the six categories in which the Messenger (peace and blessings be upon him) stipulated the two conditions mentioned earlier: currency and similarity. Paper currency today—we repeat this to fix the matter in the mind—its value is determined by gold. So when you deal in paper currency, you do not imagine that you are dealing in anything other than gold currency, because this paper has no intrinsic value. From this, we arrive at a very important issue: is zakah due on paper currencies or not? Of course, zakah is due on them, even though the matter has reached the point, unfortunately, where some people say there is no zakah on them. Some of the people who follow a madhhab, who do not have the fiqh that the Messenger (peace and blessings be upon him) intended in some of the authentic hadiths, such as his saying (peace and blessings be upon him and his family) and his supplication (peace and blessings be upon him) for his cousin 'Abdullah ibn 'Abbas . So whoever does not have fiqh says this paper currency is neither silver nor gold, so it is permissible to exchange it at different rates, and zakah is not obligatory on it except on the basis that it is from trade goods. So if we keep this reality in mind, then in this situation it is necessary to keep in mind the two conditions mentioned when exchanging one paper currency for another: that it is not permissible to exchange them at different rates. Among the problems of the present age is the rise of some paper currencies and the fall of another type of these currencies. This rise and fall, in reality, has been a cause of poverty that befalls people who are greedy for excessive, unlawful riba, or of excessive, very great wealth. And this is known to you all, with great regret.