Bring the Husk of the Old God, 2 Idols of the Sun, 5 Gold Scarabs and 5 Clay Scarabs to Vethsera inside Ahn'Qiraj. You must also attain Honored reputation with the Brood of Nozdormu to complete this quest.
The unmentionable Old God slowly awakens from his slumber beneath Ahn'Qiraj. The terrible fate that awaits Azeroth could come in days or years; time has no meaning for beings of his power.
When the stars are favorable, he will lash out against all living beings with terrible wrath. You must find him before then and find a way to bring his existence to an end.
Do this and bring me a piece of his husk. I shall grant you armor no mortal has ever worn... armor fit for one who has slain a god!