Armor of Prometheus

A protective magical force surrounds a creature of your choice that you can see within range, manifesting as spectral wild flames that covers the creature and their gear. The creature gains 5 temporary hit points for the duration. If a creature hits the affected creature with a melee attack while they have these hit points, the attacking creature takes 5 fire damage.

At Higher Levels. When you cast this spell using a spell slot of 2nd level or higher, both the temporary hit points and the fire damage increase by 5 for each slot.