Who bears the liability for money lost by a messenger when the principal's agent paid the creditor a different denomination than instructed?

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The loss of the money rests with the principal who sent the messenger. This is because the principal only instructed the messenger to collect the specified dirhams (debts) and did not authorize the substitution of a dinar for the dirhams. The exchange constitutes a transaction (sarf) requiring the creditor's consent, which was not obtained. Therefore, the messenger acted as an agent for the principal in carrying out this unauthorized exchange. Liability falls upon the principal because the loss occurred while the messenger was acting under the principal's purview for the unauthorized act. Liability shifts to the messenger only if the messenger informed the debtor that the sender permitted accepting the dinar instead of the dirhams, thereby deceiving the debtor and taking the dinar as the sender's agent.