Please clarify this situation.
My opponent has a 3/3 creature and in his turn plays an enchantment that adds +1/+1 to his creature.
I react to this with an instant, Smite The Monstrous, which states: "Destroy target creature with a power of 4 or greater."
He argues that his creature's core power is really 3, the +1 enchantment is not a permanent change - if the enchantment is exiled/countered, the creature would revert to the 3/3.
I disagree (of course), since at the time the instant was played, the creature in fact had 4 power.
Please break our disagreement and cite rules if you can. Thanks!