Pesachim 17B

(רבן) שמעון אומר: בכלים טמאין, בקרקע טהורין.

Rabban Shimon says: If the liquids were in vessels, they are ritually impure; however, if they were in the ground, they are ritually pure, as explained below.

אמר רב פפא: אפילו למאן דאמר טומאת משקין דאורייתא ⁠— משקי בית מטבחיא הלכתא גמירי לה. אמר ליה רב הונא בריה דרב נתן לרב פפא: ואלא הא דאמר רבי אליעזר: אין טומאה למשקין כל עיקר, תדע, שהרי העיד (יוסף) בן יועזר איש צרידה על משקי בית מטבחיא דכן.

Rav Pappa said: Even according to the one who says that in general the ritual impurity of liquids is by Torah law, the purity of the liquids of the Temple slaughterhouse is a halakha transmitted to Moses from Sinai, which the rabbis learned through tradition. Rav Huna, son of Rav Natan, said to Rav Pappa: But with regard to that which R' Eliezer said: There is no impurity for liquids at all by Torah law, know that this is so, as Yosei ben Yo’ezer of Tzereida testified about liquids in the slaughterhouse in the Temple that they were ritually pure. This statement indicates that liquids become impure only by rabbinic decree, a decree that is not in effect in the Temple.

ואי הלכתא גמירי לה ⁠— מי גמרינן מינה?

Rav Huna, son of Rav Natan, continued: And if they learned the ritual purity of liquids of the slaughterhouse as a halakha transmitted to Moses from Sinai through tradition, do we derive other halakhot from it? There is a principle that one cannot derive halakhic principles from halakhot transmitted to Moses from Sinai. How, then, could R' Eliezer cite this halakha as a proof for his opinion?

אמר ליה רבינא לרב אשי: והא רבי שמעון דאמר טומאת משקין דאורייתא, דתניא: רבי יוסי ורבי שמעון אומרים: לכלים טהורין, לאוכלין טמאין.

Furthermore, Ravina said to Rav Ashi, also in rejection of Rav Pappa’s statement: Isn’t it R' Shimon, who said that in general the ritual impurity of liquids is by Torah law? As it was taught in a baraita that R' Yosei and R' Shimon say: With regard to vessels that came into contact with impure liquid, the vessels are pure, as by Torah law liquids do not transmit impurity to vessels. However, with regard to foods that came into contact with impure liquid, the foods are impure, as by Torah law liquids transmit impurity to foods.