Ring of Regeneration

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.

Source: 5e Core Rules · OGL-1.0a · 5.1