This quest is not available in game.
Bring the Third and Fourth Mosh'aru Tablets to Prospector Ironboot in Tanaris.
The troll with whom you spoke did not tell the truth. The two tablets you gained for him spoke of containing the essence of Hakkar, but there is more to that legend. I have studied long, and found that there are six Tablets of Mosh'aru, not two! Six!
And I fear that we will not like what secrets the others hold..
Find the third and fourth tablets of Mosh'aru. They're in the Eastern Plaguelands, held by the mossflayer trolls. Find them, and bring them to me.