Reference for Gittin 101:20

שני שוורין קשורין מצאת והלה אומר מצאתי והחזרתי לך אחד מהן הרי זה נשבע

THE FINDER OF A LOST ARTICLE CANNOT BE REQUIRED TO TAKE AN OATH. R. Isaac said: [If a man says to another], 'You found two purses tied together,' and the other says, 'I found only one,' he can be forced to swear, [If he says,] 'You found two oxen tied together,' and the other says. 'There was only one,' he cannot be forced to swear. Why this difference? Because oxen can get loose from one another, but purses cannot.<span class="x" onmousemove="('comment',' Hence in the case of the purses the claimant could be positive, but not in the case of the oxen, and the oath is administered only if the claimant is positive. ');">¹⁹</span>

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