Historical Rules · 5 October 2018
Rule 302.6
Official source text from the 5 October 2018 Rules release
A creature’s activated ability with the tap symbol or the untap symbol in its activation cost can’t be activated unless the creature has been under its controller’s control continuously since their most recent turn began. A creature can’t attack unless it has been under its controller’s control continuously since their most recent turn began. This rule is informally called the “summoning sickness” rule.