Bekhorot 7B

הטמא״, והני נמי מינא דטמא הוא.

the non-kosher animal [min hattamei], one can infer that any type [min] of non-kosher substance is included. And these fluids, i.e., the urine of a donkey, are also a type of non-kosher substance, as they resemble the milk of a donkey, which is forbidden.

ואיכא דאמרי, דסוסים וגמלים לא קא מיבעיא להו, דלא שתו אינשי. כי קמיבעיא להו דחמור, דשתו אינשי ומעלו לירקונא, מאי?

And there are those who say there is a different version of the discussion about the urine of a donkey: With regard to the urine of horses and camels, the students of Rav Sheshet did not raise the dilemma, because people do not drink it. When they raised the dilemma it was with regard to the urine of a donkey, which people drink and which is beneficial for curing jaundice. What, then, is the halakha?

אמר להו רב ששת, תניתוה: היוצא מן הטמא טמא, והיוצא מן הטהור טהור ⁠— והני נמי מטמא קאתי.

Rav Sheshet said to them: You learned the answer to your dilemma in the Mishnah: That which emerges from the non-kosher animal is non-kosher and that which emerges from the kosher animal is kosher, and these fluids also come from a donkey, which is non-kosher. Therefore, they are forbidden.

מיתיבי: מפני מה אמרו דבש דבורים מותר? מפני שמכניסות אותו לגופן, ואין ממצות אותו מגופן.

The Talmud raises an objection from a baraita: For what reason did the rabbis say that the honey of bees is permitted? It is because they bring the nectar from the flowers into their body, but they do not excrete it from their body as a bodily excretion. So too, the urine of a donkey is not an excretion produced by the body itself. Rather, it is simply ejected in the same form that it entered the body. Why, then, should it be forbidden?