Wondrous Item, very rare
If a creature takes damage from the arrow, the creature must make a DC 15 Constitution saving throw, falling asleep for one hour on a failed save. The creature is unconscious until the effect ends, the sleeper takes damage, or someone uses an action to shake or slap the sleeper awake
Once an arrow of sleep hits a creature it becomes a nonmagical arrow.
Notes: Unconscious, Damage, Combat, Consumable