"‍There’s clearly a paradox. Money can’t be in two places at once. The money can’t be simultaneously available for withdrawal by depositors and also loaned out to the banks’ borrowers.

Therefore there’s a large element of risk in commercial banking activities. They use statistical models to insinuate that this risk is low. But the risks are more common than we think.

Suffice to say that banks are operating with an element of gharar. Gharar means uncertainty. It’s rooted in the Arabic word ‘to deceive’ (gharra). This can happen when the claim of ownership or the outcome isn’t clear. Gambling and the use of derivatives (like futures and options) are examples of gharar." - Secret Muslim Banker

From: https://www.secretmuslimbanker.com/content/the-islamic-banking-paradox