Amulet of Recall

Teleport 12 of the player's units within the targeted area to the location of the Hero when used.

This ordinary-looking piece of jewelry is made of polished silver surrounded by a ring of platinum. A series of spheres of various sizes are inscribed on the flat sides, some overlapping the others like a cluster of moons in the sky. The pattern of spheres rearranges itself periodically, so anyone familiar with the amulet sees a different arrangement each time he studies it.

Source
Arthas and Muradin Bronzebeard can buy these from a Goblin Merchant in Dissension, chapter 8 of the Warcraft III human campaign, The Scourge of Lordaeron.