Knocking Creatures Unconscious

When an adventurer reduces a monster or a DM-controlled character to 0 hit points, he or she can choose to knock the creature unconscious rather than kill it. Until it regains hit points, the creature is unconscious but not dying. Any healing makes the creature conscious.
    If the creature doesn’t receive any healing, after a short rest it is restored to 1 hit point and becomes conscious.

Published in Player's Handbook, page(s) 295, Rules Compendium, page(s) 261.