Cloak of Mirroring

The Cloak of Mirroring is a cloak that deflects all spell damage, including offensive spell like Magic Missile, but not disabling spells such as Hold Person.

Baldur's Gate II: Shadows of Amn

 * City of Caverns - dropped by a Sahuagin Priestess

In-game description
"Though it feels much like normal cloth, this shimmering cloak has on occasion been described as "woven water". Its true enchantment becomes apparent when the wearer is attacked directly by magic, and all the damage caused by spell effects is deflected harmlessly away."