Khadgar's Pipe of Insight

Grants the Hero and friendly nearby units a bonus to mana regeneration. Does not stack with Brilliance Aura.

The firsts of these pipes was carved by the arch-wizard Khadgar while he studied with the acolytes of Dalaran. Though the look of subsequent pipes of insight has varied slightly, most appear similar, with a stem of gnarled wood and a deep bowl made of yellowed bone.

Source
Arthas and Kel'Thuzad can find this in The Siege of Dalaran, chapter 7 of the Warcraft III undead campaign, Path of the Damned.