Is National Prayer Day Constitutional?

Poor Bill O'Reilly is too close-minded to see the purpose in having a separation of church and state. Why does it matter to him if there is a National Prayer Day? He is free to pray any day he wants, why does his government need to make a praying holiday? The National Day Of Prayer is obviously referring to Christianity—what if we were to have a National Worship Allah Day? Regardless of what anyone says, The National Day of Prayer was not thought up with Muslims in mind. It shouldn't be only atheists that want the separation of church and state, even though it seems as if that is the case. It's as if the religious do not understand what the alternative is.