Commentary for Exodus 23:1

לא תשא שמע שוא THOU SHALT NOT HEAR A FALSE REPORT — Take it as the Targum renders it: thou shalt not accept (listen to) a false report. This is a prohibition addressed to one who is about to accept a slanderous statement, and it is addressed also to a judge — that he should not hear the pleadings of one party to a suit before the other appears (Mekhilta d'Rabbi Yishmael 22:23:1; Sanhedrin 7b).

לא תשא...אל תשת ידך עם רשע. To sign with such people on the same document. According to Sanhedrin 23 the inhabitants of Jerusalem would not put their signature on any document unless they had satisfied themselves as to the integrity of co-signers on such documents.

לא תשא שמע שוא, this is parallel to the warning in the ninth of the Ten Commandments not to testify falsely against one’s fellow man. (Exodus 20,12) Just as the witness is warned not to perjure himself, the judges are warned not to accept such testimony. They must not listen to testimony which is patently a lie but make their own inquiries to determine if the testimony conforms to the facts. Even if there are two false witnesses already so that your testimony would not have any bearing on the outcome of the trial, you must not join them and reinforce their lies by testifying as they have done.