I have this item Mythical Soul Fragment that I got from a Labyrinth run. I have no use for it. What can I do to get rid of it from my inventory?
Cant u just drag and delete it.
No, hence the thread.
You combine three of them to get a piece of high level gear. Blizzard doesn’t allow those to be destroyed so that people don’t accidentally lose them. You can get three of them and get the piece of gear then destroy the gear, but I don’t think you are going to be able to get rid of the item.
That’s too bad. I guess I’ll have to return enough to build an item, vendor it, then never go back. 
This is from a comment on WowHead. It looks like if you just don’t take the quest you shouldn’t get one.
These are a one-per-week reward for doing the weekly quest from Wah’du at the entrance of the labyrinth. Complete the specific area for the weekly and turn it in for one fragment.
Each character is capped to one per week, and a grand total of 6 per character.
Wah’du sells mythic gear for 3 fragments per piece, so you can potentially get 2 mythic pieces of gear after 6 weeks, but that’s the limit.