This sugya discusses the nature of the ketubah and the dispute over whether the obligation is מן התורה or rabbinic. It is a central Talmudic locus for the question of ketubah de'oraita or derabbanan.
תָּנָא: הוֹאִיל וּקְנַס חֲכָמִים הוּא — לֹא תִּגְבֶּה אֶלָּא מִן הַזִּיבּוּרִית. קְנָסָא? מַאי קְנָסָא?! אֶלָּא אֵימָא: הוֹאִיל וְתַקָּנַת חֲכָמִים הוּא — לֹא תִּגְבֶּה אֶלָּא מִן הַזִּיבּוּרִית. רַבָּן שִׁמְעוֹן בֶּן גַּמְלִיאֵל אוֹמֵר: כְּתוּבַּת אִשָּׁה מִן הַתּוֹרָה. וּמִי אָמַר רַבָּן שִׁמְעוֹן בֶּן גַּמְלִיאֵל הָכִי? וְהָתַנְיָא: ״כֶּסֶף יִשְׁקֹל כְּמֹהַר הַבְּתוּלוֹת״: שֶׁיְּהֵא זֶה, כְּמוֹהַר הַבְּתוּלוֹת, וּמוֹהַר הַבְּתוּלוֹת כָּזֶה. מִכָּאן סָמְכוּ חֲכָמִים לִכְתוּבַּת אִשָּׁה מִן הַתּוֹרָה. רַבָּן שִׁמְעוֹן בֶּן גַּמְלִיאֵל אוֹמֵר: כְּתוּבַּת אִשָּׁה אֵינָהּ מִדִּבְרֵי תוֹרָה, אֶלָּא מִדִּבְרֵי סוֹפְרִים!
§ A Sage taught in a baraita: Since payment of the marriage contract is a penalty instituted by the Sages, she may collect only from the husband’s land of the most inferior quality. The Gemara asks: A penalty? What penalty is there in a marriage contract? Rather, emend the baraita and say: Since it is a rabbinic ordinance and not a Torah obligation, she may collect only from the husband’s land of the most inferior quality. Rabban Shimon ben Gamliel says: The marriage contract of a woman is an obligation by Torah law. The Gemara asks: And did Rabban Shimon ben Gamliel say that? But isn’t it taught in a baraita that it is written with regard to a seducer: “He shall pay money according to the dowry of virgins” (Exodus 22:16)? The Torah establishes that this fine will be like the dowry of a virgin, and that the dowry of a virgin will be like this fine, i.e., fifty silver sela, or two hundred dinars. From here the Sages based their determination that a woman’s marriage contract is an obligation by Torah law. Rabban Shimon ben Gamliel says: The marriage contract of a woman is not an obligation by Torah law, but is by rabbinic law.