Bava Metzia 7 - Two People Found a Document
If two persons, a creditor and a debtor, appear in court holding on to a note of indebtedness, and the creditor says, "It is mine: it fell from me and I subsequently found it," but the debtor says, "It was indeed yours, however I repaid the debt to you," - then the witnesses who appear on the document must certify that the document is indeed authentic, and they divide it with an oath, just like in the case of a garment.
Why is the certification needed if the debtor admits that the document is valid? Because if we believe him on that, we should also believe that he repaid, or else we need to confirm the document independently.
Art: Anglo French Convention signed in London, by Oswaldo Meaulle Tofani