What is the liability of an agent who takes a pledge on behalf of the principal to collect a debt, and the pledge subsequently perishes while in the agent's possession?

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The agent is not liable for the loss of the pledge. This ruling is based on the understanding that taking a pledge in this manner constitutes an invalid pledge (rahn fasid). The physical possession (qabd) in an invalid contract is treated like possession in a valid contract. Therefore, assets that are not guaranteed when possessed under a valid contract (such as a pledge taken without express permission) are not guaranteed when possessed under an invalid contract.