D&Dtools

You must cast this spell in the same round when you
attempt a smite attack. If the attack hits, you deal an
extra 2d6 points of damage to the target of the smite.
Whether or not you succeed on the smite attempt, during
each subsequent round of the spell’s duration, you deal
an extra 2d6 points of damage on any successful melee
attack against the target you attempted to smite. The
spell ends prematurely after any round when you do not
attempt a melee attack against the target you previously
attempted to smite, or if you fail to hit with any of your
attacks in a round.