Armor of Orthys

A protective magical force surrounds you, manifesting as a shimmer of heat and dancing embers that surround 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 level

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