Is it permissible to hire a person to skin an animal using the hide itself as payment?

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The contract is invalid (lam yajuz). This is due to the uncertainty regarding whether the hide will emerge intact, its thickness, or its quality. Furthermore, what is invalid as a price in a sale is invalid as consideration in a lease contract, similar to other unknown variables. If the slaughterer skins the animal under this invalid agreement, he is entitled to the customary wage (ajr mithl).