This quest was marked obsolete by Blizzard and cannot be obtained or completed.
Bor Wildmane at Cenarion Hold in Silithus wants you to destroy an Abyssal Templar and bring him an Abyssal Crest as proof of the deed.
We've seen the Twilight's Hammer cultists performing rituals to summon powerful elemental nobles. We don't know if these are the beings the cultists worship or if they act as intermediaries to even more powerful forces. One thing is for sure: they are receiving orders from these elementals.
I want you to find a way to contact an Abyssal Templar and give it a proper beating! Nothing throws the troops in disarray like taking out the chain of command. Bring back proof while you're at it.