Free translation from the rambam, hilchos melochim perek yud aleph halacha aleph;
“In the future, the Messianic king will arise and renew the Davidic dynasty, restoring it to its initial sovereignty. He will build the Temple and gather the dispersed of Israel…Anyone who does not believe in him or does not await his coming, denies not only the statements of the other prophets, but those of the Torah and Moses,” i.e., apikorus