Breakfast with Solomon - Proverbs 6:1
"My son, if you have become surety for a neighbor,
have given a pledge for a stranger"
This is the classic passage against co-signing a note for someone so that your financial health is in the hands of another person. Its application can also be stretched to be against borrowing in general, or striking surety, or making a pledge even for yourself.
One should not be involved in promising to pay the debts of another. If a person is not able to secure the necessary financing on their own, it is because they are a bad risk. It is this type of risk or exposure that leaves you completely at the whim, foolishness, or sloth of another.