• Magic Dust
• Item Level 20Disenchants into:
  Not disenchantable
• Requires Level 10
• Use: Puts the enemy target to sleep for up to 30 sec. Any damage caused will awaken the target. Only one target can be asleep at a time.
• 1 Charges
• Sell Price: 2 13

Source

This item drops from Dust Devil in Westfall.

Patch changes

• Patch 3.1.0 (14-Apr-2009): Magic Dust now has a 10 second PvP duration. 
  

External links

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