Stoneskin

4th-Level Transmutation Spell (Artificer, Druid, Ranger, Sorcerer, Wizard)

Casting Time: Action
Range: Touch
Components: V, S, M (diamond dust worth 100+ GP, which the spell consumes)
Duration: Concentration, up to 1 hour

Until the spell ends, one willing creature you touch has

If you have Resistance to a damage type, damage of that type is halved against you (round down). Resistance is applied only once to an instance of damage. See also Damage and Healing.

to Bludgeoning, Piercing, and Slashing damage.

Source: Player's Handbook, p. 321