Avodah Zarah 36B

״במארה אתם נארים ואתי אתם קבעים הגוי כלו״, אי איכא גוי כולו ⁠— אין, אי לא ⁠— לא.

It is the verse: “You are cursed with the curse, yet you rob Me, even this whole nation” (Malachi 3:9). This teaches that if there is the acceptance of the whole nation, yes, an ordinance may be instituted, but if not, no, the ordinance may not be instituted.

גופא, אמר באלי אמר אבימי נותאה משמיה דרב: פיתן ושמנן, יינן ובנותיהן ⁠— כולן משמונה עשר דבר הן. בנותיהן מאי היא? אמר רב נחמן בר יצחק: גזרו על בנותיהן נידות מעריסותן.

§ The Talmud discusses the matter itself: Balei says that Avimi of Nota says in the name of Rav: The prohibitions with regard to non-Jews’ bread and their oil, their wine and their daughters, are all from the 18 matters issued in a single day in the time of the students of Shammai and Hillel. The Talmud asks: With regard to their daughters, what is the decree? R' Naḥman bar Yitzḥak says: They decreed upon their daughters that they should be classified as menstruating women from the time they are in their cradle, i.e., they decreed that from when they are young, non-Jew women are always considered to be menstruating.

וגניבא משמיה דרב אמר: כולן משום עבודה זרה גזרו בהן, דכי אתא רב אחא בר אדא אמר רבי יצחק: גזרו על פיתן משום שמנן, מאי אולמיה דשמן מפת?

The Talmud presents another opinion. And Geneiva says in the name of Rav: non-Jews’ bread, oil, wine, and daughters were all decreed upon due to the concern that Jews might participate in idol worship with non-Jews as a result of intermingling with them. As, when Rav Aḥa bar Adda came from Eretz Yisrael to Babylonia he said that R' Yitzḥak says: They decreed a prohibition upon their bread due to their oil. The Talmud asks: In what way is the prohibition with regard to oil stronger than the prohibition with regard to bread? That is, why does the primary concern relate to the oil of non-Jews rather than their bread?