Yosef Karo, Shulchan Aruch — Choshen Mishpat 41
“ Paragraph 4- If one had a documented debt owed by his counterparty and he lost the document but the witnesses are accessible, and the borrower claims he paid back, the borrower would be believed with a heses oath even if a kinyan was made. The borrower is believed with a heses oath to say he paid back even if the payment deadline had not passed because the lender no longer possesses the document and we are concerned that the borrower paid back, which is why the document was ripped up or burnt. ”
