• The Black Book
• Item Level 76Disenchants into:
  [Nexus Crystal]: 1-2
• Binds when picked up
• Unique
• Trinket
• Classes: Warlock
• Requires Level 60
• Use: Empowers your pet, increasing its spell power by 200, its attack power by 325, and its armor by 1600 for 30 sec. This spell will only affect an Imp, Succubus, Voidwalker, Felhunter, or Felguard.
• Sell Price: 7 20 39

Source

This item drops from Razorgore the Untamed in Blackwing Lair.

Patches and hotfixes

• Patch 1.7.0 (13-Sep-2005): The effect tooltip for The Black Book now properly lists the duration. 
  
• Patch 1.6.0 (12-Jul-2005): Added 
  

External links

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