The financing commodity should be purchased from a third party. The financier should not simply buy an asset from the client and immediately resell the same asset to him through a pre-arranged buy-back. That circular structure lacks the genuine third-party purchase that gives the transaction commercial substance.
This rule is especially important in financing because cost-plus sale (مرابحة) is valid only when the financing remains a real sale. The sequence of ownership, possession, risk and final sale must therefore be visible in the transaction.