הלכה על סנהדרין 5:2

The commandment to judge with righteousness: To judge with righteousness, as it is stated (Leviticus 19:15), "you shall judge your people with righteousness." And the explanation of it comes that the judges were commanded to treat the parties to the dispute equally - meaning to say that the judge not honor one of the litigants more than the other. And so they said in Sifra, Kedoshim, Chapter 4:4 that one not speak all that he needs, and [the judge] say to the other, "Speak briefly." And so [too,] in the chapter [entitled] Shevuot HaEdut (Shevuot 30a), "Our Rabbis learned, '"You shall judge your people with righteousness" - that it not be that one stand and one sit; one not speak all that he needs, and [the judge] say to the other, "Speak briefly."'" And so [too,] included in this commandment is that every man that is wise in the laws of the Torah and righteous in his ways is commanded to judge the law of the Torah between parties of a dispute, if he has the power in his hand [to do so]. And even an individual can judge from Torah writ - and like they, may their memory be blessed, said (Sanhedrin 3a), "One can judge his fellow from Torah writ, as it is stated, 'You shall judge your people with righteousness.'" But the sages warned (Mishnah Avot 4:8), that a man not judge alone. And also included in this commandment is that it is fit for every person to judge his fellow favorably, and only to understand his deeds and his words favorably.