Dreambane

As you cast this spell, you curse a creature within range. That creature must attempt a Wisdom saving throw. On a failure, it is cursed. While subjected to this curse a creature is incapable of falling asleep. It can no longer gain any benefits from taking a long rest and automatically suffers one level of exhaustion every two days it goes without sleep. 

This spell has no effect on creatures that doesn't normally sleep, like elves, fiends and elementals.