PHB pg 272

Sanctuary

1-level Abjuration

You ward a creature within range against attack. Until the spell ends, any creature who targets the warded creature with an attack or a harmful spell must first make a Wisdom saving throw. On a  failed save, the creature must choose a new target or lose the attack or spell. This spell doesn't protect the warded creature from area effects, such as the explosion of a fireball. If the warded creature makes an attack casts a spell that affects an enemy, this spell ends.