Mishneh Torah — Transmission of the Oral Law מסירת תורה שבעל פה, Chapter 34

וּדְבָרִים הַלָּלוּ, בְּדִינִים וּגְזֵרוֹת וְתַקָּנוֹת וּמִנְהָגוֹת שֶׁנִּתְחַדְּשׁוּ אַחַר חִבּוּר הַתַּלְמוּד. אֲבָל כָּל הַדְּבָרִים שֶׁבַּתַּלְמוּד הַבַּבְלִי, חַיָּבִין כָּל בֵּית יִשְׂרָאֵל לָלֶכֶת בָּהֶם; וְכוֹפִין כָּל עִיר וְעִיר וְכָל מְדִינָה וּמְדִינָה לִנְהֹג בְּכָל הַמִּנְהָגוֹת שֶׁנָּהֲגוּ חֲכָמִים שֶׁבַּתַּלְמוּד, וְלִגְזֹר גְּזֵרוֹתָם וְלָלֶכֶת בְּתַקָּנוֹתָם.

These [principles apply regarding] the judgments, decrees, ordinances, and customs which were established after the conclusion of the Talmud. However, all the matters mentioned by the Babylonian Talmud are incumbent on the entire Jewish people to follow. We must compel each and every city and each country to accept all the customs that were put into practice by the Sages of the Talmud, to pass decrees parallelling their decrees, and to observe their ordinances, since all the matters in the Babylonian Talmud were accepted by the entire Jewish people.