Yosef Karo, Shulchan Aruch — Choshen Mishpat 47
“ The lender is not even believed where he is negatively impacting himself too, such as where the document is for 200 and he only owes others 100. If after the lender said the document was given on trust, he paid back his creditor and he now wants to use this document to collect from the borrower we analyze the situation. ”
