Dark Whispers( Elder Evils, p. 12)
By whispering foul utterances in the Dark Speech, you can drive your enemies insane.
Dark Speech (BV) ,
In addition to the basic uses of the Dark Speech, you can whisper words of incredible wickedness to form grotesque visions in the minds of those who hear you. All living creatures within a 30-foot radius that can hear your words must make Will saves (DC 10 + 1/2 your character level + your Cha modifi er). On a failure, creatures with fewer Hit Dice than you are staggered for 1d10 rounds; those with as many or more Hit Dice are confused for 1 round. This is a mind-affecting, supernatural effect.
Whenever you use Dark Speech in this manner, you take 1 point of Charisma damage.
You gain a +2 circumstance bonus on saving throws made when someone uses the Dark Speech against you. This bonus stacks with the +4 circumstance bonus from Dark Speech.
If you cannot take ability damage, you cannot select this feat.