What is the ruling on exchanging a Dinar for ten Dirhams when only five Dirhams are present?

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If a man exchanges one Dinar for ten Dirhams but possesses only five Dirhams, the exchange is invalid if the parties separate before the full ten Dirhams are received. If they take the five Dirhams and separate, the exchange regarding half the Dinar is voided. Imam Ahmad stated the rulings on these matters. If the parties wish to rectify the situation, they must either dissolve the exchange for the portion lacking a counter-value or dissolve the entire contract. They may then contract separately: buying half a Dinar for five Dirhams, making the payment, receiving the full Dinar (where the purchased half is his, and the remainder is a trust), and then separating. Subsequently, dealing with the remaining portion of the Dinar via exchange, sale, future-sale (salam), gift, or agency is permissible.