Vow of Nonviolence( Book of Exalted Deeds, p. 47)
You have taken a sacred vow to avoid violence against humanoids.
Sacred Vow (BE) ,
Vow of Peace (BE) ,
The saving throw DC for spells you cast or other special abilities you use against humanoid or monstrous humanoid targets is increased by +4 if the spell does not deal damage (including ability damage but not nonlethal damage), bestow negative levels, or cause death. Spells affected by this feat include most Abjuration, Enchantment, and Illusion spells (though not phantasmal killer, for example), those few Divination spells that have targets and require saving throws (including detect thoughts and discern lies), and even Necromancy spells such as waves of fatigue and ray of exhaustion. It does not affect most Evocation, Conjuration, and Transmutation spells. The bonus granted by this feat does not stack with the bonus granted by the Spell Focus feat. It affects only saving throw DCs, not caster level checks or other elements of a spell. The benefit of this feat extends to special abilities other than spells that allow a saving throw, but only if the ability does not deal damage and is not dependent on dealing damage. For example, a character with the Stunning Fist feat can increase the saving throw DC to avoid being stunned by +4 if she deals nonlethal damage, rather than regular damage, with her stunning attack. A couatl's venom would not become more virulent because of this feat, however, because it deals ability damage and requires the couatl to deal hit point damage in order to deliver it.
To fulfill your vow, you must not cause harm or suffering to humanoid or monstrous humanoid foes. You may not deal real damage or ability damage to such foes through spells or weapons, though you may deal nonlethal damage. You may not target them with death effects, disintegrate, pain effects, or other spells that have the immediate potential to cause death, suffering, or great harm. Your purity is so great that any ally of yours who slays a helpless or defenseless foe within 120 feet of you feels great remorse. Your ally takes a -1 morale penalty on his attack rolls for 1 hour per your character level. For each helpless foe slain, the attack penalty increases by 1, to a maximum equal to your character level. The duration of the increased penalty starts from the latest slaying. You may ask your allies to give you an oath that a helpless foe will not be slain. If the oath is sworn, an ally who later breaks the oath takes the penalty for doing so as if you were present. If you leave a helpless foe to be killed by your allies, you have broken your vow. You may ask a defeated creature to give you an oath of surrender or noninterference in exchange for its life. If the creature breaks this oath to you, you can allow your allies to deal with the creature as they see fit without breaking their oaths or your vow of nonviolence. If you intentionally break your vow, you immediately and irrevocably lose the benefit of this feat. You may not take another feat to replace it. If you break your vow as a result of magical compulsion, you lose the benefit of this feat until you perform a suitable penance and receive an atonement spell.