Bava Metzia 95B

דכתיבא בהדיא ⁠– קתני, דאתיא מדרשא ⁠– לא קתני.

that is explicitly written in the Torah he teaches, and those matters that are derived through interpretation he does not teach. Consequently, no proof can be brought from the Mishnah.

תא שמע: שאלה ושאל בעליה עמה, שכרה ושכר בעליה עמה, שאלה ושכר בעליה עמה, שכרה ושאל בעליה עמה, אף על פי שהבעלים עושין מלאכה במקום אחר, ומתה ⁠– פטור.

The Talmud suggests: Come and hear a proof from a baraita: If one borrowed an animal and borrowed the services of its owner with it, or rented it and hired its owner with it, or borrowed it and hired its owner with it, or rented it and borrowed the services of its owner with it; in all of these cases, although the owner performed the work for him in another place, i.e., not near the animal, and it dies, the borrower or renter is exempt.

סברוה הא מני ⁠– רבי יהודה היא, דאמר: שוכר כשומר שכר דמי! והא האי תנא קתני מילתא דאתיא מדרשא, ואילו שומר חנם לא קתני!

The Talmud notes: The scholars in the study hall assumed that this baraita is in accordance with whose opinion? It is in accordance with the opinion of R' Yehuda, who says that one who rents an item is responsible for it like a paid bailee. According to his understanding, the baraita teaches that the exemption from liability applies to both a borrower and a paid bailee. Consequently, the baraita can serve as a proof: Doesn’t this tanna teach even a matter that is derived through interpretation, i.e., the fact that exemption from liability applies to a paid bailee, while he still does not teach that it applies to an unpaid bailee? It would appear that this is a proof that exemption from liability does not apply to an unpaid bailee, since it does not apply to a mishap that is the result of the bailee’s negligence.