Devout Aurastone Hammer

Heirloom Item
Heirloom items scales to the level of the character it is being worn on. It should last most classes to level 80 and can be mailed to a person's alternate character if they are on the same account.

Source
This item is sold by the following vendors for :
 * in Dalaran
 * in Dalaran
 * in Dalaran
 * in Stormwind City
 * in Orgrimmar

Since Patch 3.2.0, it can be sold by the following vendor for :
 * at the Argent Pavilion in Icecrown

The can also be used but does not have quite as useful statistics.