Is being a guarantor or cosigning a loan halal?
Guaranteeing someone's debt is itself a virtuous act. Kafalah is a recognised contract in Islamic law, it is treated as a form of assistance to a person in need, and a guarantor may not charge a fee for providing it precisely because it is meant to be a favour rather than a service sold. The difficulty is not the guarantee but what is being guaranteed. Standing behind an interest-bearing loan means enabling a transaction scholars prohibit and becoming a party to the documentation, and narrations name the parties to a riba contract - including those who write and witness it - as sharing in the blame. Most scholars therefore advise against guaranteeing conventional loans. There is a widely recognised exception where a family member faces genuine necessity and no alternative exists. Beyond the ruling, there is a practical warning worth stating plainly: as guarantor you owe the entire debt if the borrower defaults, and most guarantors do not realise this until they are asked to pay.