Voice of Dread

You whisper in a dead language a secret to the universe that targets a creature's lifeforce. A creature you can see must make a Constitution Saving Throw. On a failed saved the creature receives 1 level of exhaustion for a number of rounds equal to the spell level. On a successful save, a creature can not be targeted by this spell for 24 hours. 

At Higher Levels: When you cast this spell at higher levels, the exhaustion effect last for the same number of rounds as the level cast. In addition, for every level this spell is cast past 4th level, you may have the creature roll and additional Constitution Saving Throw to add another level of exhaustion. Once the creature passes a saving throw, it loses all levels of exhaustion.