Reference for Bava Metzia 3:2
הַשּׂוֹכֵר פָּרָה מֵחֲבֵרוֹ וְהִשְׁאִילָהּ לְאַחֵר, וּמֵתָה כְדַרְכָּה, יִשָּׁבַע הַשּׂוֹכֵר שֶׁמֵּתָה כְדַרְכָּה, וְהַשּׁוֹאֵל יְשַׁלֵּם לַשּׂוֹכֵר. אָמַר רַבִּי יוֹסֵי, כֵּיצַד הַלָּה עוֹשֶׂה סְחוֹרָה בְּפָרָתוֹ שֶׁל חֲבֵרוֹ, אֶלָּא תַחֲזֹר פָּרָה לַבְּעָלִים:
If one hired a cow from his neighbor and lent it to another [with the owner's permission (for we rule that one watcher who gives to another without permission is liable)], and it died normally, the hirer swears [to the owner] that it died normally, [and he is exempt from payment, a hirer being exempt (from payment) for accidents (like death)], and the borrower, [who is liable for accidents] pays the hirer. R. Yossi said: If so, he (the hirer) "does business" with his neighbor's cow! Rather (payment for) the cow is returned to the owner. [The halachah is in accordance with R. Yossi.]