Translation:Shulchan Aruch/Choshen Mishpat/38
Paragraph 1- If two witnesses testified about an individual that he owed so and so a maneh and two others come and contradict or impeach the witnesses, the alleged borrower is exempt. If witnesses testified in court that one owed his adversary a maneh and they later said they testified falsely, their original testimony stands because once they testify they cannot re-testify. They are, however, believed with respect to themselves and they must pay whatever loss they caused the defendant. The Mechaber summarized in an area where he should have discussed at length. Although we do not judge the laws of impeached witnesses today because it is a fine, there is still a practical importance to the laws in that an impeached witness can no longer testify as was explained above in Siman 34, whereas witnesses who were merely contradicted are valid witnesses as was explained above in Siman 31. Thus, the author of the Tur wrote a significant amount of rules regarding impeached witnesses and anyone who wants to study them should look there.