Soul-Collar of the Incarnate

Soul-Collar of the Incarnate is the Tier 4 cloth head armor for shadow priests and gives bonuses to stamina, intellect, spirit and overall spell damage. It is available through token item that drops in Karazhan.

Source
This item is sold by in the Seer's Library on the Scryer's Tier and by  in the Shrine of Unending Light on Aldor Rise in Shattrath City. The cost of the item is a token.