This quest is not available in game.
Archmage Lan'dalock in Dalaran wants you to return with a Fragment of the Black Knight's Soul.
This quest may only be completed on Heroic difficulty.
My counterpart, Archmage Timear, has asked me to warn you of something dire. Soon, you will be participating in the Trial of the Champions at the Argent Coliseum in Icecrown. You must beware of interference from one known only as the Black Knight.
Bring me a fragment of his soul that the Kirin Tor will know he is dealt with. I am told that failing to do so will be your own undoing.