—namely through increase (ziyāda) and through deferment (nasīʾa).

In any act of currency exchange (ṣarf) it is impermissible to delay hand-over for even an hour or more, nor may either party disappear from the other before mutual possession has taken place. No transfer of debt (ḥawāla), no surety (ḍamān), no option to rescind (khiyār), no waiting period, indeed no form of deferment whatsoever is allowed. The only lawful manner is “Here it is, and here it is,” with both parties taking possession in the same sitting and at the same moment.

According to Imām Mālik, it is not permissible to exchange against money that you do not yet possess, or against something that is not physically present with you—even if it is brought before you separate. The proper procedure, in Mālik’s view, is that each of the two parties produces the actual specie he wishes to buy from the other; they take possession, then part ways, with no liability remaining between them. Should any portion of the exchange be delayed, whatever has already been taken is invalid in Mālik’s judgment, and the entire transaction is void if it was a single deal.

If someone exchanges dirhams and they come up short by one dirham, and the other party wishes to lend him that missing dirham so that the exchange may be completed—treating it as a debt he can later reclaim—this is not permissible. Even if he were to gift him that dirham afterward, once he knows such an arrangement is unlawful, it would still be impermissible. In such a case the exchange must be annulled and each party must recover what he had paid.

Likewise, if the two exchangers separate after lawfully concluding their deal, and one of them then discovers that what he received is deficient, falling short of his due, the ruling is as follows: if he demands completion, the exchange is annulled the moment he takes the remainder; if he is content with the deficiency, the exchange stands. The same applies if he finds the coins he received are of inferior quality and the other party acknowledges the defect: the exchange is void and each party reclaims his payment; but if he accepts the defect, their exchange remains valid.

All of this holds when the exchange was contracted as a single lump sum without assigning a separate price to each dinar. If, however, several dinars are exchanged for dirhams and a distinct price is named for every dinar, and then among the dirhams he later discovers a dinar and wishes to return it, only the exchange involving that one dinar is annulled, to the extent of the dirhams actually exchanged for that single dinar or less.