Historical Rules · 12 July 2019
Rule 701.2a
Official source text from the 12 July 2019 Rules release
To activate an activated ability is to put it onto the stack and pay its costs, so that it will eventually resolve and have its effect. Only an object’s controller (or its owner, if it doesn’t have a controller) can activate its activated ability unless the object specifically says otherwise. A player may activate an ability if they have priority. See rule 602, “Activating Activated Abilities.”