Mishneh Torah — Transmission of the Oral Law מסירת תורה שבעל פה, Chapter 24

וְעִנְיַן שְׁנֵי הַתַּלְמוּדִין – הוּא פֵּרוּשׁ דִּבְרֵי הַמִּשְׁנָה וּבֵאוּר עֲמוּקוֹתֶיהָ, וּדְבָרִים שֶׁנִּתְחַדְּשׁוּ בְּכָל בֵּית דִּין וּבֵית דִּין מִיְּמוֹת רַבֵּנוּ הַקָּדוֹשׁ וְעַד חִבּוּר הַתַּלְמוּד. וּמִשְּׁנֵי הַתַּלְמוּדִין, וּמִן הַתּוֹסֶפְתָּא, וּמִסִּפְרָא וּמִסִּפְרֵי, וּמִן הַתּוֹסֶפְתּוֹת – מִכֻּלָּם יִתְבָּאַר הָאָסוּר וְהַמֻּתָּר, וְהַטָּמֵא וְהַטָּהוֹר, וְהַחַיָּב וְהַפָּטוּר, וְהַכָּשֵׁר וְהַפָּסוּל, כְּמוֹ שֶׁהִעְתִּיקוּ אִישׁ מִפִּי אִישׁ מִפִּי מֹשֶׁה מִסִּינַי.

The intent of both the Talmuds is to elucidate the words of the Mishnah, to explain its deeper points, and [to relate] the new matters that were developed by each court from the era of Rabbenu Hakadosh until the composition of the Talmud. From the entire [body of knowledge stemming from] the two Talmuds, the Tosefta, the Sifra, and the Sifre, can be derived the forbidden and the permitted, the impure and the pure, the liable and those who are free of liability, the invalid and the valid as was received [in tradition], one person from another, [in a chain extending back] to Moses at Mount Sinai.