Bava Batra, Chapter Ten, Mishnah Five
Mishnah five deals with laws concerning paying back debts.
1) If a man had paid part of his debt and gave the debt document to a third party, and the debtor said to him, If I have not paid you back by such and such a day, give him (the creditor) back the debt document and the time came and he had not paid, Rabbi Yose says: He should give it to him.
a) Rabbi Judah says: He should not give it to him.
When a person borrows from another person the creditor keeps possession of the debt document, in order to use it later to collect his debt. If the debtor were to pay back half of the loan, the creditor would not be able to give back the debt document, lest he be unable to collect the second half of the loan. On the other hand, the debtor would not want the creditor to keep the document, lest he use it to collect the entire loan, even though half was already paid back. One solution to such a problem was to give the debt document to a third person and for the debtor to promise to pay back the remainder within a certain time or else the third party was to return it to the creditor. According to Rabbi Yose in such a case if the time elapsed the third party should give the debt document to the creditor. According to Rabbi Judah he should not. Since the debtor did not really intend to allow the creditor to collect more than his debt by using the debt document after it had been partially paid, the third party is not allowed to return it to the creditor.