Arabic (قلب الدين) for debt restructuring or debt roll-over or refinancing of an existing debt/ dayn (postponement or extension of maturity date of a debt against some form of an increase). More specifically, it involves postponement of a due debt whether it resulted from a loan (qardh) or its amount was the price in a deferred-payment sale (bai’ muajjal/ bay’ muajjal) or otherwise in justification for an increase in the debt amount. In this sense, it is tantamount to the type of riba that pre-Islamic Arabs used to charge and pay (riba al-jahiliyyah) which is prohibited by shari’ah.

Qalb-ul dayn may also involve the postponement of a due debt in return for some benefit (increase in the amount of debt/ principal, or any other form of benefits, whether in kind or as services). This increase can be attained through a fictitious transaction– i.e., one that is not intended for itself but rather as a means (legal ruse/ hilah) to circumvent a prohibition. Qalb-ul dayn is prohibited by shari’ah, whether the debtor (madeen) is solvent or not.

It is also known as ba’y al-dayn bil dayn or faskh al-dayn bil dayn.