Well, tell us *why* you are fasting: we can't determine how doing something will impact your goals if you haven't told us what your goals are.
If you are fasting for health reasons, do not take the whey protein. You *want* your body to a) detox as much as possible, which is achieved by not having to deal with processing wastes from digestion, and b) you actually WANT your body to autolyze tissue because the thing is smart and starts with the crappiest, faultiest stuff. You want the crap tissue autolysed, and replaced with good tissue which you will build from clean eating. Plus, c), yes you will lose muscle mass, but not that much. People are so weak at the end of fasts not because of the muscle loss but because of all the water weight and electrolytes that comprise a good part of the weightloss.
If your goal is health, don't freak out over the muscle loss. Really. If you're worried your BMR will fall, worry not: the decrease from muscle loss ONLY is around 100 cal/day, which is a slice of processed cheese, you can live life with one less slice of processed cheese daily.
If you are fasting to get lean, you should go to a bodybuilder forum. These folks have developed tons of systems for getting fat down, "lean gains" comes to mind. The people who developed them did so in order to maximize muscle definition, and with 0 concern for the health consequences.
Long story short, it depends on your goal-- but no.