When is the combination of a loan and a sale permissible?

It is not permissible to combine a loan (salaf) and a sale, due to the prohibition of the Prophet, peace and blessings be upon him, against it. This is unanimously forbidden and serves as a means of blocking the path to usury (riba). The majority of scholars broaden this prohibition to include combining a loan with any other commutative contract, such as leasing. If there is favoritism or an increase in price, then that constitutes usury; otherwise, it is forbidden as a means of blocking the path to usury.