Reference for Ketubot 209:12

ואגר בטילא מי שרי והתניא מכוער הדיין שנוטל שכר לדון אלא שדינו דין ה"ד אילימא אגר דינא דינו דין והתניא הנוטל שכר לדון דיניו בטילין אלא אגר בטילא וקתני מכוער הדיין

But [is a judge] permitted to take compensation for loss of work? Was it not in fact taught: Contemptible is the judge who takes a fee for pronouncing judgment; but his decision is valid? What is the precise situation? If he took a fee for acting as judge how could his decision be valid, have we not taught: One who takes wages for adjudicating, his judgments are void? Consequently it must mean a fee for loss of work, and yet it was stated, was it not, “Contemptible is the judge etc.”?

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