Summary

Yosef Karo Shulchan Aruch — Choshen Mishpat 37

A person is disqualified from any testimony in which he gains some kind of benefit by testifying. Therefore, if two people are partners in land and a third party attempts to remove the land from one of the partners by claiming that the individual who sold the land to them had originally stolen it from him, the other partner may not testify on behalf of his partner to disqualify the plaintiff’s witnesses. His testimony would not even help for his partner’s portion unless he removed himself from the field and they made a kinyan to give his portion to this partner.
Source: Wikisource

Yosef Karo Shulchan Aruch — Choshen Mishpat 37

If Reuven sold an unsecured cow or garment to Shimon and Yehuda brings a claim against Shimon to remove the item from his possessions on the basis that Reuven obtained it from a thief, Reuven may testify for Shimon because he gets no benefit if the item remains in the hands of Shimon since Reuven’s creditor may not collect moveable items, even if they were designated as the method of collection. In modern times, even if the borrower were to place a lien on moveable items together with real property, the lender would still not be able to collect from the moveable items that were sold.
Source: Wikisource

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