Ring of Regeneration

From Dungeon Master's Guide, page 191. Found on Magic Item Table H.

Description
Ring, very rare (requires attunement).

While wearing this ring, you regain 1d6 hit points every 10 minutes, provided that you have at least 1 hit point. If you lose a body part, the ring causes the missing part to regrow and return to full functionality after 1d6+1 days if you have at least 1 hit point the whole time.