Mishpatim: Rishpei Aish and The Holy Besht: Mitzvah 81 – Concept 574
“Do not extend your hand with the wicked to be a venal witness.” (Exodus 23:1) We may not accept the testimony of transgressors. (Rambam, Hilchot Eidut – The Laws of Evidence)
Treasuring Speech:
Do not speak negatively of others, thereby joining with Satan in his accusations against Israel, and becoming a partner with the most venal witness of all. (Rabbi Mordechai of Neshchiz – Rishpei Aish)
Never be stingy in words of praise of another. (The Baal Shem Tov – Sefer HaSichot)