This quest is not available in game.
Travel to the continent of Teldrassil and find Malfurion's agent somewhere outside the walls of Darnassus.
This is a journey of redemption, hero. Would it be that I was slain today, I would have died for a just and righteous cause. You must recover the green scepter shard. You must cleanse Eranikus of the taint placed upon him by the Old Gods.
Travel to Darnassus. Just outside the city walls you will find one of my agents. This agent will set things in motion for us and inform Tyrande of our plans without alerting Staghelm.
A fall from grace a thousand years in the making...