Seek the aid of the Knights of the Ebon Blade in Acherus above the Broken Isles.
If we are to infuse the shard's power into the Ashbringer we will need help. We cannot wield such dark magic; however, I know who can...
The Knights of the Ebon Blade.
I will commission a flight for you to Acherus at once and meet you there - find Aludane Whitecloud in Dalaran when you are ready.