Merciful (3.5e Flaw)
From D&D Wiki
Prerequisite: Good alignment
Summary: Many times you don't have it in your heart to kill.
Effect: Whenever your character is in combat and delivers a blow to an enemy that brings it below 0 hit points and dying, but not killed, you must make a Will save (DC 15 + 1/2 your character level) or be forced to attempt to stabilize that enemy immediately. You gain a +2 bonus on this saving throw for every additional enemy you can see within 30 feet, and a +4 bonus whenever stabilizing that enemy would be obviously dangerous to yourself or others, or a +8 if outright and unquestionably suicidal.
Benefit: Bonus Feat