You send yourself or a beast or humanoid you can see within range into a magical sleep. A target other than yourself must have 5 current hit points or less. An unwilling creature with a Wisdom score of 11 or higher can make a Wisdom saving throw. On a success, it is unaffected by the spell. A creature affected by this spell falls unconscious and prone for the duration.  

At the end of each of its turns, a sleeping target can make (or repeat) the Wisdom saving throw. On a success, the target gains 1d3 temporary hit points and the spell ends. The spell also ends if there is a loud noise, the sleeper takes damage, or if someone uses an action to shake the creature awake.  The target gains no temporary hit point if it doesn't wake up by succeeding on the saving throw. 

While the creature has the temporary hit point granted by this spell, its exhaustion level is reduced by 1. This benefit lasts for 1 hour and ends early if the temporary hit points are lost or replaced with temporary hit points from another source.

The number of hit points the spell can affect for a target other than you increases when you reach higher levels. At 5th level, you can affect a beast or humanoid with 15 current hit points or less. At 11th level, you can affect a beast or humanoid with 25 current hit points or less. At 17th level, you can affect a beast or humanoid with 40 current hit points or less.  

Rule Tip 

Temporary hit points aren’t cumulative. If you have temporary hit points and receive more of them, you don’t add them together, unless a game feature says you can. You decide which temporary hit points to keep. (PHB p. 198)