Combusting Revival

When the dagger of renewal absorbs a creatures soul it charges one slot for the spell to be used. Taking the dagger you must strike the body of a creature wich the dagger has absorbed the soul to within 12 hours of the absorption. The dagger will then begin to blaze and burn forcing the body to combust into flames and ash. all creatures within 15 ft. must make a dexterity saving throw of 18 or higher or take 4d6 of fire damage.