Historical Rules · 4 February 2011
Rule 502.2
Official source text from the 4 February 2011 Rules release
Second, the active player determines which permanents he or she controls will untap. Then he or she untaps them all simultaneously. This turn-based action doesn’t use the stack. Normally, all of a player’s permanents untap, but effects can keep one or more of a player’s permanents from untapping.