Talmud for Pirkei Avot 1:8
יְהוּדָה בֶן טַבַּאי וְשִׁמְעוֹן בֶּן שָׁטָח קִבְּלוּ מֵהֶם. יְהוּדָה בֶן טַבַּאי אוֹמֵר, אַל תַּעַשׂ עַצְמְךָ כְעוֹרְכֵי הַדַּיָּנִין. וּכְשֶׁיִּהְיוּ בַעֲלֵי דִינִין עוֹמְדִים לְפָנֶיךָ, יִהְיוּ בְעֵינֶיךָ כִרְשָׁעִים. וּכְשֶׁנִּפְטָרִים מִלְּפָנֶיךָ, יִהְיוּ בְעֵינֶיךָ כְזַכָּאִין, כְּשֶׁקִּבְּלוּ עֲלֵיהֶם אֶת הַדִּין:
Yehudah ben Tabbai and Shimon ben Shetach received it from them. Yehudah ben Tabbai says: Do not you, [(a judge)], make yourself like [those] orchei hadayanim [(lawyers), who arrange ("orchim") cases for the litigants before the judges, it being forbidden for one (a judge) to reveal his judgments to one of the litigants, telling him: Do thus and thus so that you win your case — even if he knows that he is in the right. Alternately, "ke'orchei hadayanin," like the great among the judges. This, in reference to a disciple sitting before his master, that he not make himself like the great among the judges, to speak before his master as a decisor of the law. "Orchei" as in "the erkaoth of the gentiles," the erkaoth of the House of David." And from others I have heard: "Do not make yourself as the great ones of the judges to force the litigants to come to judgment before you.] And when litigants stand before you, let them be in your eyes like wicked ones, [that you not favor one of them, saying "This one is a distinguished man and will not make a false claim." For if you say this, you will see no guilt in him.], and when they take their leave of you, let them be innocent in your eyes when they have taken the judgment upon themselves. [Do not suspect the arraigned one as a thief but as one who erred and had no intention of stealing. Or, if an oath was imposed upon one of them and he swore, do not say that he swore falsely.]