Instructions
Accept the quest from David Wayne in eastern Terokkar Forest. You must complete the "Bane of the Illidari" quest before "Quenching the Blade" becomes acceptable. Shadowmoon Valley lies to the east of Terokkar and is accessible on foot or through the air with a flying mount.
Continue flying east once you enter Shadowmoon Valley. You'll eventually come upon pools of green lava and a large, rock formation standing in the middle. Fly toward the rock formation, which is known as the Hand of Guldan. On the northern side of the Hand of Gul'dan, you will see more green pools. Fly to those pools and land to discover The Scalding Pools.
Open your inventory and right-click the Forged Illidari-Bane Blade. Your character will submerge the blade into The Scalding Pools. In turn, you will receive the Quenched Illidari-Bane Blade.
Go back to David Wayne. Right-click him to turn in the quest and choose your reward.