Endurance Utility 16Diehard
Though blood pours from a dozen wounds, you refuse to lie down and die.
Immediate Interrupt Personal
Trigger: You drop to 0 hit points or fewer
Effect: Until you aren’t dying or until the end of the encounter, the dying condition doesn’t cause you to fall unconscious, but you are dazed.
Published in Player's Handbook 3, page(s) 169.