Reference for Bava Kamma 210:5

שואל אני עליו חייב שהרי פטר עצמו ממתה מחמת מלאכה

for he would thereby have released himself from any liability were the animal to have died merely because of the usual work performed with it.<span class="x" onmousemove="('comment',' Which is a valid defence in the case of a borrower but not in that of a thief. ');">⁶</span> Now, this surely proves that though the animal now stands intact, since if it were to be stolen<span class="x" onmousemove="('comment',' In the case he swore he was an unpaid bailee. ');">⁷</span>

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