The Seal of Danzalar

The Seal of Danzalar is an epic ring. It is one of the few items with resilience that drops from a raid boss. This is a PvP/Arena ring for casters.

Source
This item drops from The Lurker Below in Serpentshrine Cavern.

Trivia
The Seal of Danzalar is a reference to Buffy: The Vampire Slayer's Seal of Danzalthar. The phrase "From beneath you it devours" appears frequently in the second episode of the seventh season named "Beneath You".