Historical Rules · 25 August 2017
Rule 302.7
Official source text from the 25 August 2017 Rules release
Damage dealt to a creature by a source with neither wither nor infect is marked on that creature (see rule 119.3). 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 701.13, “Regenerate”) and during the cleanup step (see rule 514.2).