What is the ruling on guaranteeing an interest-bearing loan while the guarantor is unaware of its prohibition, and what are the implications for repentance? And what is the ruling on taking an interest-bearing loan with a small interest rate for marriage, knowing that not getting married might lead to committing forbidden acts?

The questioner must free himself from his guarantee for his brother in the usurious bank, because usury is one of the gravest sins, and cooperation in it is a sin and aggression, as Allah Almighty says: (And cooperate in righteousness and piety, but do not cooperate in sin and aggression) and the Prophet, peace and blessings be upon him, said: "They are equal in sin." What is unlawful remains unlawful, whether little or much, and usury is only resorted to in cases of extreme necessity that cannot be averted except by it.