Reference for Ketubot 185:2

איכא דאמרי אפי' באחריות נמי דאמר ליה אחוי טירפך ואשלם לך:

There are those who say: [This is so] even where no guarantee was given, since [Reuven] may say to him [to the creditor], “I do not want Shimon to have any grievance against me.”

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