One of the most celebrated days for Chabad Lubavitch Chassidim comes as a result of a vicious Mesira by fellow Jews.
On the 19th of Kislev of the year 5559 from creation (1798), Rabbi Schneur Zalman of Liadi — a leading disciple of Rabbi DovBer of Mezeritch and the founder of Chabad Chassidism — was released from his imprisonment in the Peter-Paul fortress in Petersburg, where he was held for 53 days on charges that his teachings threatened the imperial authority of the Czar. More than a personal liberation, this was a watershed event in the history of Chassidism heralding a new era in the revelation of the “inner soul” of Torah, and is celebrated to this day as “The Rosh Hashanah of Chassidism.”
Links: About Kislev 19
19. He redeemed my soul in peace from battles against me, because of the many who were with me. 20. May God-He who is enthroned from the days of old, Selah-hear and humble those in whom there is no change, and who do not fear God. 21. He extended his hands against his allies, he profaned his covenant. 22. Smoother than butter are the words of his mouth, but war is in his heart; his words are softer than oil, yet they are curses. 23. Cast your burden upon the Lord, and He will sustain you; He will never let the righteous man falter. 24. And You, O God, will bring them down to the nethermost pit; bloodthirsty and treacherous men shall not live out half their days; but I will trust in You.