A sale (bay‘) in which both payment and delivery are deferred. In other words, it is the sale of a debt for a debt. It belongs to the class of forbidden sales (buyu’ batilah). This was supported by the hadith (prophetic tradition) forbidding the exchange of a delayed counter-value for another delayed counter-value.

There are five forms of this sale mentioned in the books of fiqh, the most well-known of which is the exchange whereby a lender extends a debtor’s repayment period in return for an increase in the debt amount (the principal). The increase on the principal amounts to interest (riba).

In Arabic, bay’ alkali bil kali means credit for credit or a loan against a loan or deferment of al-badalain (two countervalues).

It is also known as bay’ aldayn bil dayn.