Player's Handbook, pg. 216
4-level Abjuration
Life-preserving energy radiates from you in an aura with a 30-foot radius. Until the spell ends, the aura moves with you, centered on you. Each non-hostile creature in the aura (including you) has resistance to necrotic damage, and its hit point maximum can't be reduced. In addition, a non-hostile, living creature regains 1 hit point when it starts its turn in the aura with 0 hit points.