He who is surety for a stranger will suffer, but one who hates being surety is secure. (Proverbs 11:15)
Proverbs repeatedly warns against guaranteeing a loan, and especially for a stranger. It is not only unwise business; it can do much harm in every realm. It is biblically acceptable to lend another money, but it is to be done without concern for restitution: the attitudes being, if you cannot afford to give it, do not lend it. Making a modern day loan is an investment. Lending to a stranger is a bad investment. There is no history or relationship on which to fall. You've got to love the Bible's business sense. Proverbs, furthermore, clearly warns, "Do not be one of those who shakes hands in a pledge, one of those who is surety for debts." Remember, surety is the act of guaranteeing another's debt or responsibility. There is only one who did it correctly and that One was Christ. "Jesus has become a surety of a better covenant."