Translation:Shulchan Aruch/Choshen Mishpat/63
Paragraph 1- If one produces a loan document on another and two witnesses come and say that the plaintiff asked us to forge this document for him, we would not allow the plaintiff to ever collect with this document, even if its signatures have been verified, unless the witnesses on the document testify that they saw the loan or others testify that they saw these witnesses sign the document. If the witnesses on the document testify that this is their signature, the plaintiff may collect with it. There are those that disagree and hold that recognizing the signatures is of no effect.
Paragraph 2- When the Rabbis said that one cannot collect with a document, we do not leave it in the plaintiff’s possession. Rather, we give it to a third party. If the witnesses did not say that the plaintiff asked us to forge this document, but an unspecified document, all of the plaintiff’s documents would be suspect and he would not be able to collect with them.