Asbagh it must be annulled. Perhaps Ibn al-Qāsim’s statement concerns a case in which they have not negotiated the rate, but one merely says to the other, “Come with me so that I may exchange money with you.” Asbagh’s statement would then concern a case in which they have negotiated the rate, with one saying, “Come with me so that I may exchange your gold at such-and-such a rate.”
As for an assignment of payment, where someone concludes a currency exchange and refers another person to the money changer to collect the proceeds, this is impermissible according to Ibn al-Qāsim unless he himself takes possession of the proceeds and hands them to the person he referred. If the latter collects them, it is impermissible, even in his presence and before he leaves the money changer. This differs from agency: if, after concluding the exchange, he appoints an agent to collect the dirhams, and the agent collects them in both parties’ presence before his principal departs, it is permissible. It also differs from assigning payment of the original sum upon rescission of a food-purchase contract.
Sahnūn and Ashhab held that it is permissible if the person referred collects the proceeds in the presence of the person who referred him, before the latter departs. This is like assigning payment of the original sum upon rescission of a food-purchase contract, or appointing an agent who collects the proceeds before the parties separate.
If, however, the principal or the person assigning payment leaves before the agent or the person referred takes possession, the currency exchange is invalid. This is agreed upon in the case of assignment, but disputed in the case of agency. For Abū Zayd related from Ibn al-Qāsim that when two men exchange dirhams they jointly own for a dinar from another man, and one of them leaves while the other remains to collect the dinar, this is permissible. A similar ruling appears in Asbagh’s transmissions—unless a distinction is drawn between the two cases on account of their joint ownership of the dirhams or dinars. Such a distinction is far-fetched, however, since he treats the two cases alike in al-Mudawwana.
As for appointing an agent to collect the original payment upon rescission of a food-purchase contract, this is permissible even if the contracting parties separate, provided that the agent collects it before parting from the seller under the advance-payment contract.
As for a guarantee, it is permissible if it covers the dinars should a third party establish ownership of the dirhams, or the dirhams should a third party establish ownership of the dinars. Otherwise, it is impermissible. The same applies to a pledge. Success comes from Allah, glorified and exalted is He.