Pirkei Avot
About JIYF
While a judge, do not act as an advocate;
While the litigants stand before you,
regard them both as guilty;
But when they leave, having accepted the judgment,
regard them both as innocent.
—Yehudah ben Tabbai

Examine the witnesses thoroughly,
and be careful in your words,
lest they learn from them to lie.
—Shimon ben Shetach

Translation note (1:8,9): These begin: “Yehudah ben Tabbi and Shimon ben Shetach received from them.”
The following, 4:9 and 4:10, are the other two sayings in Avot about acting as a judge in court. In 4:10 'They' refers to the other judges voting on a case.

He who refrains from judging frees himself
from animosity, robbery and false oaths;
He who rules brashly is foolish, wicked, and crass.
—Rabbi Ishmael

Do not judge alone, for none can judge alone except One.
And do not say: Accept my opinion!
For they are entitled, not you.
—Rabbi Ishmael