Common Courtesy
Enchantment
Oracle Text
Whenever a player casts a spell without asking your permission while casting it, counter that spell. When a player asks you permission to cast a spell and you refuse, counter that spell and sacrifice this enchantment.Rulings (1)
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Wizards of the CoastYou do have to ask yourself permission to cast spells, although you can give yourself a one-time permission that applies to all future spells you cast.