The Black Book

• The Black Book
• Item Level 29Disenchants into:
  Not disenchantable
• Binds when picked up
• Unique-Equipped
• Trinket
• 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.
• Classes: Warlock
• Requires Level 25
• Sell Price: 7 20 39

Source

This item drops from Razorgore the Untamed in Blackwing Lair.

Patch changes

• Patch 2.0.3 (2007-01-09): Now provides a flat amount of spell power, attack power, and armor to your pet, instead of by a percentage.
  
• Patch 1.7.0 (2005-09-13): The effect tooltip for The Black Book now properly lists the duration.
  
• Patch 1.6.0 (2005-07-12): Added.
  

External links

• Wowhead
• WoWDB