Harry Potter - Secrets of Hogwarts

You attempt to interrupt a being you can see in the process of casting a spell. If the creature is verbally casting a spell of 3rd level or lower, its spell fails and has no effect. If it is verbally casting a spell of 4th level or higher, make an ability check using your spellcasting ability. The DC equals 10 + the spell’s level. On a success, the creature’s spell fails and has no effect. On a success or if the being was casting the spell non-verbally, the target must cast all other spells non-verbally until the end of its next turn. If it tries to cast a spell verbally, it must first succeed on an Intelligence saving throw, or the casting fails and the spell is wasted.