What is a good scripture I can use when my mother in law keeps telling me to give the shirt off my back for?

My wife's sisters' boyfriend has a less than stellar driving record. He has no insurance and just totaled his car. We have a spare vehicle that is too old to get any money out of so we keep it as a back up if we have mechanical issues with our car. We have heard that bad things could happen and we could get sued if he wrecks our car and obviously, our insurance record would take a hit. My mother in law keeps telling me that I need to give the shirt off of my back for others and let him borrow the car. Because she speaks in biblical scriptures only, can someone please give me some advice or biblical scriptures that I can reference in order for her to have an understanding of why we're looking out for our own interest and that letting him borrow the car could be detrimental to our insurance and finances if we get sued due to his poor driving? Thank you.