when the term falls due.
Before that date arrives you may not accept, in place of what is owed, anything of lesser quality—even if it is of the same kind—for that is the practice known as daʿ wa taʿajjal (remit part of the debt in return for early payment), and it amounts to riba. Apply this principle to every case that falls under the same heading.
Likewise, you may not take part of the merchandise owed to you before its due date while converting the remainder into its cash price; Malik regarded this as reprehensible and impermissible. If, however, you take part of the goods and leave the rest until its appointed time, that is allowed. There is also no harm in accepting, for part of your claim, whatever goods you wish—whatever the commodity may be—before maturity, provided the balance remains deferred until the term, whether the goods arise from a salam contract or from a loan.
Malik held that with respect to all items that may lawfully be sold before one has taken possession of them, it is permissible to accept from your debtor whatever he offers in settlement, so long as it differs from the commodity originally owed and you receive it on the spot. If delivery is deferred, the transaction becomes an exchange of one debt for another, which is prohibited.
Should someone enter into a salam of goods for goods, and the buyer seeks to rescind the contract in return for adding something extra, that is permissible provided the goods have not perished and can be returned in their very form, and provided the additional amount is paid immediately, whatever its nature, whether the salam term has fallen due or not. If that extra amount is deferred, it is merely debt for debt.
If the original goods have perished and he wishes to substitute similar goods plus any addition, that is impermissible, whether or not the due date has arrived. Even if, before maturity, he gives the increment taken from the very same merchandise—some portion of it—that too is not allowed; but once the term falls due he may receive the addition, whether from that merchandise or from something else. All of this applies only when the additional amount is paid immediately; if it is deferred, it is not permissible.
Whoever advances payment in a salam for wheat and meat, or for anything edible or potable, and the seller then brings it to him