Armor of Avernus

A protective infernal force surrounds you, manifesting as a shadowy flame that covers you and your gear. You gain 5 temporary hit points for the duration. If a creature hits you with a melee attack while you have these hit points, the 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 level above 1st.