The scholars are unanimously agreed that guarantee is permissible in principle.

The public interest in fact calls for it; indeed, need and even necessity may require it. It is a form of mutual assistance in righteousness and piety, a means of fulfilling a Muslim’s need and relieving his distress.

For a guarantee to be valid, the guarantor must be legally competent to dispose of property, for he is undertaking a financial obligation; therefore it is invalid if offered by a minor or by a spendthrift who has been placed under interdiction. His consent is also a condition: if he was compelled to act as guarantor, the guarantee is void, because it is a gratuitous assumption of another’s liability, and—like any gift of property—requires voluntary acceptance.

Guarantee is a contract intended to benefit and assist the person guaranteed; hence it is unlawful to take payment for it. Receiving remuneration for a guarantee resembles a loan that brings benefit: once the creditor demands payment, the guarantor must settle the debt on behalf of the principal debtor, after which he will recover the amount from that debtor in the form of a loan—thus the guarantee would have generated a profit for the guarantor. Such arrangements must be avoided; the object of a guarantee should be cooperation and kindness, not exploitation or burdening the needy.

A guarantee is valid with any wording that conveys the required meaning, such as: “Ana ḍamīn” (I am guarantor), “Ana qabīl,” “Ana ḥamīl,” “Ana zaʿīm,” or statements like “Taḥammaltu daynak” (I have assumed your debt), “Ḍamintuhu” (I have guaranteed it), or “Huwwa ʿindī” (It is with me). The Lawgiver did not restrict it to a particular formula, so custom determines sufficiency.

The creditor has the right to demand payment from whomever he wishes—either the guarantor or the principal debtor—because the obligation rests upon both of them; he may therefore pursue whichever of the two he chooses, in accordance with the Prophet’s statement: