Rashi on Deuteronomy 17:11/רש"י על דברים י״ז:י״א

1ימין ושמאל [THOU SHALT NOT DEPART FROM THE WORD WHICH THEY SHALL TELL THEE] TO THE RIGHT NOR TO THE LEFT, even if he (the judge) tells you about what appears to you to be right that it is left, or about what appears to you to be left that it is right, you have to obey him; how much the more is this so if actually he tells you about what is evidently right that it is right and about what is left that it is left (cf. Sifrei Devarim 154:5).