Rambam lists the 13 Principles as the beliefs which measure one's merits for the world to come, and he writes it as an elaboration of the Mishnaic statement: "All of the Jewish people, have a share in the World-to-Come" (see Rambam_on_Mishnah_Sanhedrin.10.1.16).
Does Rambam refer to those principles elsewhere in his other works?