Regarding the issue of currency, it appears there is a consensus among economists that currency is no longer weighed in gold and silver as it was in the past.

The questioner : Shaykh, regarding the issue of currency now, I feel that, as it were, there is a consensus among economists that currency is no longer weighed in gold and silver as it was in the past, but rather external policies now intervene in it. Otherwise, how is the price of the currency determined? So, on this basis, if we say that the operative cause of riba does not extend beyond the six categories, then do the categories of riba and sales that are not permissible apply to this currency?

The Shaykh : First, there is scholarly disagreement regarding the six categories: are they exclusive, or do they accept additions? Those who say they are exclusive are the Zahiris and their followers, whereas the majority of scholars include other matters in them, and the criterion in that is what is measured by volume or weight.

The questioner : All right, Shaykh, no problem if there is evidence?

The Shaykh : It is this hadith in al-Bukhari, as well as what is measured by volume or weight.
As for this paper currency,
Allahu Akbar, Allahu Akbar
As it is said: behind the dune there is what is behind it; so what is behind the statement mentioned just now? That is, that there is no riba of excess in it, and no zakah on it? What is intended?

The questioner : It is to arrive at the permissibility of all the currencies that exist now; because if they say this statement, which is that they have restricted the operative cause to the six categories as Ibn Hazm (may Allah have mercy on him) said, then they must refute the fact that these forbidden sales do not apply to it.

The Shaykh : In any case, this pillar has collapsed.

The questioner: Yes.

The Shaykh: Yes.