• Belt of the Twilight Assassin
• Item Level 226Disenchants into:
  [Abyss Crystal]: 1-2
• Binds when picked up
  
• Leather
• Waist
• 333 Armor
• +84 Agility
  +84 Stamina
• Durability 40 / 40
• Requires Level 80
• Equip: Improves hit rating by 49.
  Equip: Increases your expertise rating by 57.
  Equip: Increases attack power by 124.
• 

Source

This item is sold by the following vendors for 28 :

•  Arcanist Firael <Emblem of Conquest Quartermaster> in Dalaran
•  Hexil Garrot <Tools of the Trade> in Dalaran
•  Magister Sarien <Emblem of Conquest Quartermaster> in Dalaran
•  Valerie Langrom <Leather Armor Merchant> in Dalaran

Patch changes

• Patch 3.1.0 (14-Apr-2009): Added. 
  

External links

• Battle.net (EU)
• Wowhead
• Thottbot
• WoWDB