Is the profit resulting from buying and selling foreign currencies in a joint bank account, which the bank approved and disbursed, considered unlawful wealth merely because the bank later claimed it made an error in determining the prices?

Selling currencies is permissible with real or constructive possession, such as a bank transfer or a certified check. Regarding the seller's claim of a mistake in the price, scholars have differed: some do not accept his word without proof, while others accept it with his oath, giving the buyer the option [to proceed or cancel]. Still others accept it if the seller is known for his truthfulness, while some do not accept it even with the buyer's confirmation. The word "seizure" has no effect, as what matters are the facts.