Nether-Stalker Mah'duun has tasked you with the deaths of 4 Shattered Hand Centurions. Return to him in Shattrath's Lower City once they all lie dead in order to collect the bounty.
Do you question your master? Neither does Mah'duun.
The blood of the centurions of the Shattered Hand clan is what I seek. You will find them within the Shattered Halls of Hellfire Citadel.
If you want the bounty, you will not return until you have slain them all.