Mishneh Torah — Transmission of the Oral Law מסירת תורה שבעל פה, Chapter 14

וְהוּא קִבַּץ כָּל הַשְּׁמוּעוֹת וְכָל הַדִּינִין וְכָל הַבֵּאוּרִין וְהַפֵּרוּשִׁין שֶׁשָּׁמְעוּ מִמֹּשֶׁה רַבֵּנוּ, וְשֶׁלִּמְּדוּ בֵּית דִּין שֶׁלְּכָל דּוֹר וָדוֹר, בְּכָל הַתּוֹרָה כֻּלָּהּ; וְחִבַּר מֵהַכֹּל סֵפֶר הַמִּשְׁנָה. וְשִׁנְּנוֹ בָּרַבִּים, וְנִגְלָה לְכָל יִשְׂרָאֵל; וּכְתָבוּהוּ כֻּלָּם, וְרִבְּצוּ בְּכָל מָקוֹם, כְּדֵי שֶׁלֹּא תִשְׁתַּכַּח תּוֹרָה שֶׁבְּעַל פֶּה מִיִּשְׂרָאֵל.

He collected all the teachings, all the laws, and all the explanations and commentaries that were heard from Moses, our teacher, and which were taught by the courts in each generation concerning the entire Torah. From all these, he composed the text of the Mishnah. He taught it to the Sages in public and revealed it to the Jewish people, who all wrote it down. They spread it in all places so that the Oral Law would not be forgotten by the Jewish people.