This quest is not available in game.
Travel to the Undercroft - at the southernmost section of the Eastern Plaguelands - and recover Taelan's Hammer. Return to Tirion Fordring upon completion of your objective.
To help Taelan regain what he has lost, you must gather items from his past.
The first such item is a toy that I gave to him on his 7th birthday. It was his most cherished possession: A miniature war hammer; an exact replica of my very own.
After I was banished for treason, his mother told him that I had died. He was taken to my false grave at the Undercroft, where he buried the hammer along with my memory - forever.
You must venture to the Undercroft and recover Taelan's hammer.