Wand of Negation

Dispels all magical effect in a target area. Deals 200 damage to summoned units.

Source
Arthas receives one in Blackrock & Roll, chapter 2 of the Warcraft III human campaign, The Scourge of Lordaeron, by defeating a Gnoll.

Furion can find one in Brothers in Blood, chapter 5 of the night elf campaign, Eternity's End.