Soridormi at Caverns of Time wants you to retrieve Vashj's Vial Remnant from Lady Vashj at Coilfang Reservoir and Kael's Vial Remnant from Kael'thas Sunstrider at Tempest Keep.
Seven vials were drawn from the Well of Eternity by Illidan. He poured three into the lake on top of Mount Hyjal and a second Well of Eternity was created. For years the rest were believed lost.
With the opening of the Dark Portal, we've come to know that he gave one each to his lieutenants Kael'thas and Vashj. Retrieve what remains of them; we will need them as foci to open a gateway to any events tied to Mount Hyjal, recent or ancient. The outcome of the Battle of Mount Hyjal must be preserved.