give (someone) the shirt off (one's) back

Translations
отдать последнее
He's so generous, he'd give you the shirt off his back if you needed it.
Он такой щедрый, что отдал бы тебе последнее, если бы тебе это понадобилось.
Definitions
To be extremely generous and willing to give everything one has to help someone else, often to the point of self-sacrifice.