What is the ruling on a sale where the buyer agrees to purchase a slave on the condition that a third party will pay a portion of the price (e.g., 'Sell your slave to so-and-so, on the condition that I owe five hundred [dirhams]')?

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Such a sale is void (fasid) because the entire price must be incumbent upon the buyer. Stipulating that part of the price be the obligation of another party invalidates the transaction because the seller cannot prevent the transfer of the item while the price liability rests with someone else. This situation differs from saying, 'Free your slave, or divorce your wife, and I owe five hundred,' because the latter involves compensation in exchange for the cessation of the marriage bond or the ownership of the slave, which is permissible in marriage cancellation but not in property transfer where the compensation rests with a non-party.