Historical Rules · 16 January 2016
Rule 502.2
Official source text from the 16 January 2016 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.