Kingdoms in Death
Undead you raise or create harbor a retributive curse that is unleashed if they are destroyed.
Benefit: Each undead you raise or create with any necromancy spell releases a burst of negative energy upon its destruction, dealing 1d6 points of damage plus an additional 1d6 points per 2 Hit Dice to every creature within a 10-foot spread (Refl ex DC 15 half). This damage comes from negative energy, and it therefore heals undead creatures
Rulebook: Libris Mortis (p. 26)
Edition: Supplementals (3.5)