Historical Rules · 1 October 2009
Rule 506.4
Official source text from the 1 October 2009 Rules release
A permanent is removed from combat if it leaves the battlefield, if its controller changes, if an effect specifically removes it from combat, if it's a planeswalker that's being attacked and stops being a planeswalker, or if it's an attacking or blocking creature that regenerates (see rule 701.11) or stops being a creature. A creature that's removed from combat stops being an attacking, blocking, blocked, and/or unblocked creature. A planeswalker that's removed from combat stops being attacked.