Historical Rules · 1 October 2009
Rule 302.7
Official source text from the 1 October 2009 Rules release
Damage dealt to a creature by a source without wither is marked on that creature. If the total damage marked on that creature is greater than or equal to its toughness, that creature has been dealt lethal damage and is destroyed as a state-based action (see rule 704). All damage marked on a creature is removed when it regenerates (see rule 701.11, "Regenerate") and during the cleanup step (see rule 514.2).