Kael's Vial Remnant

Kael's Vial Remnant is a quest item required for attunement to the Battle for Mount Hyjal wing in the Caverns of Time. It is said that Illidan Stormrage took seven vials of water from the Well of Eternity before its destruction. Three were poured into the lake at the top of Mount Hyjal, but the other four were believed to have been lost. It was revealed that Illidan gave one each to his two top lieutenants, Kael'thas Sunstrider and Lady Vashj.

This item is required for the following quest:


 * The Vials of Eternity

Source
Kael's Vial Remnant drops from in the Eye of Tempest Keep.