Mage Armor

1st-level abjuration
Casting Time: 1 action
Range: Touch
Components: V, S, M (a piece of cured leather)
Duration: 8 hours

You touch a willing creature who isn’t wearing armor, and a protective magical force surrounds it until the spell ends. The target’s base AC becomes 13 + its Dexterity modifier. The spell ends it if the target dons armor or if you dismiss the spell as an action.

Spell Lists. Sorcerer, Wizard

Source: Player's Handbook, Dungeon Master's Guide