its replacement. All of this, according to their view, applies within the exchange session, provided that the parties have not separated with knowledge of the matter.

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If someone asks, “If an involuntary delay invalidates currency exchange according to Mālik, and a shortfall cannot be waived, how can defective coins be accepted? They are equivalent to a shortfall, since the agreement was to exchange only sound coins; receiving defective coins therefore amounts to receiving nothing.” The answer is that, according to Mālik and most of his companions, if particular dinars and dirhams are specified in a currency exchange, the contract becomes tied to those coins. If none are specified, the contract becomes tied to particular coins either upon receipt or when the parties separate. Defective coins may therefore be accepted, because the exchange has become tied to them through one of these two forms of designation.

This explains their disagreement concerning dirhams to which a third party establishes ownership at the time of the exchange: must the money changer provide their exchange value from the money remaining in his possession to which no third-party claim has been established? Those who hold that the contract becomes tied to particular coins upon receipt do not oblige him to do so unless he wishes, in which case it constitutes a new exchange. Those who hold that it becomes tied to particular coins only when the parties separate oblige him to do so. This differs from ordinary sales, in which the monetary payment is not tied to particular coins unless they are specified—and whether specifying them makes the contract binding upon those particular coins is itself disputed.

Those who permit replacement hold that dinars and dirhams in currency exchange do not become tied to the contract unless they are specifically designated, and that an involuntary delay does not invalidate the exchange. This has already been discussed.

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It has already been stated that currency exchange permits neither an option to rescind, nor a prior arrangement, nor an assignment of payment, nor a pledge, nor a guarantee. As for an option to rescind, there is no disagreement that it renders the exchange invalid, whether both parties have the option or only one of them, because the option prevents immediate settlement between them. As for a prior arrangement, it is disliked. If, however, such an arrangement is made and the exchange is then concluded on that basis, Ibn al-Qāsim holds that it is not annulled, while according to