Yosef Karo, Shulchan Aruch — Choshen Mishpat 22
“ Paragraph 1- One who accepts a relative or disqualified individual to be a judge or witness- acceptance means they accepted to be judged; handing the money over to a third party to judge is not called acceptance- like two valid witnesses or three expert judges, even if he is disqualified due to sin, whether the party accepted to forfeit his rights and forgive what his counterparty was claiming based on their words or he accepted that he will give his adversary whatever he is claiming on the basis of this disqualified person’s testimony or ruling, if they made a kinyan, he cannot retract. ”
