Nether-Stalker Mah'duun wants you to kill 3 Malicious Instructors. Return to him in Shattrath's Lower City once they all lie dead in order to collect the bounty.
Mah'duun has heard it said that none are as cruel as the six-armed demonesses inside the Shadow Labyrinth.
Go to Auchindoun, seek them out, kill them all.
If you cannot accomplish so simple a task, we do not have anything further to say to one another.