give the shirt off back
give (someone) the shirt off (one's) back
To act in a very generous and selfless manner. I'm not surprised that Tammy loaned you money—she would give anyone the shirt off her back.
give someone the shirt off one's back
Fig. to give anything that is asked for, no matter the sacrifice required. Tom would give any of his old army buddies the shirt off his back. You can always count on Mark when you're in trouble; he'd give you the shirt off his back.