Witch Hunter's Armor
Armorrare
A suit of this armor is typically etched or embroidered with protective glyphs and runes. While wearing this armor, you gain a +1 bonus to AC, and you have advantage on saving throws against spells. If you fail a saving throw against a spell while wearing this armor, you can choose to succeed instead. If you do, the armor's magic ceases to function until the next dawn.
Source: Vault of Magic · OGL-1.0a · 5.1