What is the ruling on guaranteeing a person who has taken a murabaha loan from an Islamic bank for the purpose of finishing a residential apartment?

The fundamental principle regarding surety (kafalah) and guarantee (dhaman) is that they are permissible acts. They are contracts of donation and beneficence, and their performer is rewarded if their intention is good.

Thus, if the surety is based on a murabaha contract that fulfills the conditions of validity, then the guarantor has performed a praiseworthy act according to Sharia and will be rewarded for it if they intended it for the sake of Allah, regardless of whether the guaranteed party intends to finish an apartment for dwelling or another permissible matter.

However, if the murabaha contract does not fulfill the conditions of validity, then surety is not permissible due to its involvement in assisting in sin, as Allah Almighty says: "And cooperate in righteousness and piety, but do not cooperate in sin and aggression." The consideration is for realities, not names, even if the bank considers itself an Islamic bank.