Q 2: I know that getting a loan from a bank is Haram (prohibited) as it is regarded as Riba (usury/interest). My question does not deal with this point; rather I ask
whether the warrantor of the person who takes out a loan is sinful.
Knowing that this warrantor is religiously- committed, keen to avoid the forbidden acts and never dealt with Riba-based (usurious) banks.
Taking out loans from the bank with an interest is regarded as Riba which is Haram in Islam. It is impermissible for the warrantor to warrant the one who deals in Riba as this involves encouraging committing a forbidden act and helping in sin which is prohibited by Allah who says:
...but do not help one another in sin and transgression.
(Part No. 13; Page No. 298)
May Allah grant us success. May peace and blessings of Allah be upon our Prophet Muhammad, his family and Companions!