Invader's Scourgestone

Invader's Scourgestones are small talismans that are taken from the stronger willed Scourge. The Argent Dawn will accept the Scourgestones as proof of your willingness to fight the Scourge. Scourgestones may be turned in to Nicholas Zverenhoff at Light's Hope Chapel, Argent Officer Garush at The Bulwark, or Argent Officer Pureheart at Chillwind Camp.

Source
This item drops from stronger Scourge in the Western Plaguelands, the Eastern Plaguelands, Scholomance and Stratholme. You must have the Argent Dawn Commission, the Seal of the Dawn, or the Rune of the Dawn equipped to pick up the Scourgestones.

Invader's Scourgestone as a quest objective
This item is an objective for the following quests: