The Rambam stated that the tenth red heifer will be prepared by the Messiah:
וְהָעֲשִׂירִית יַעֲשֶׂה הַמֶּלֶךְ הַמָּשִׁיחַ מְהֵרָה יִגָּלֶה אָמֵן כֵּן יְהִי רָצוֹן: [Mishneh Torah, Parah Adumah 3:4]
Is he the originator of this prediction, and if not, what is his source?