Reference for Bava Metzia 197:5

אמר לך רב לא תימא נעשה כאמר ליה אלא אימא באמר ליה הכישה במקל והיא תבא

For it has been stated: [If A said to B,] 'Lend me your cow;' and he asked him, 'By whose hand shall [I send it]?' to which he replied, 'Strike it with a stick, and it will come,' said R. Nahman, in the name of Rabbah b. Abbuha in Rab's name: Once it leaves the lender's possession and it dies, he [the borrower] is responsible.

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