Reference for Bava Metzia 195:5
וסיפא בג' דא"ל ג' פרות נתתי לך ב' בשאילה ואחת בשכירות ומתו הני תרתי דשאילה ואמר ליה שואל אין חדא דשאילה מתה אידך לא ידענא אי דשאילה מתה ודקיימא דשכירות היא אי דשכירות מתה והא דקיימא דשאילה היא ומתוך שאינו יכול לישבע משלם
the first clause is possible only when three, and the second when four [animals are involved]. 'The first clause when three [are involved]': A said to B, 'I gave you three cows, half a day on loan and half on hire, (or, [he says, I gave you them] one day, on loan and one on hire,) and the three died, all in the period when they were borrowed.' To which the borrower replied, 'As for one, the claim is entirely unfounded [I never received it]; the second did die in the period when it was borrowed; of the third, I do not know whether it died during the time it was borrowed or the period when it was hired.' Since he cannot swear, he must pay.