You attempt to interrupt a creature in the process of Casting a Spell. If the creature is Casting a Spell of 3rd level or lower, its spell fails and has no effect. If it is 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.

At Higher Levels: When you cast this spell using a spell slot of 4th level or higher, the interrupted spell has no effect if its level is less than or equal to the level of the spell slot you used.