Ring of Regeneration
Ring,
Very Rare
(requires attunement; cost 35000 gp)
Crafting Components
Vial of troll blood
While wearing this ring, as long as you have at least 1 hit point you regain 1d6 hit points every 10 minutes. As long as you have at least 1 hit point the entire time, when you lose a body part over the next 1d6 + 1 days it completely regrows and you regain full functionality.
Source