وَلَا يُصَلَّى الْوِتْرُ بِجَمَاعَةٍ فِي غَيْرِ شَهْرِ رَمَضَانَ.
Translation: And witr is not performed in congregation outside the month of Ramadan.
The rule concerns the regular communal arrangement of witr. In the Hanafi practice, congregational witr is attached to the Ramadan tarawih arrangement.
The negation should not be read as making every conceivable occasional non-Ramadan congregation categorically invalid; jurists distinguish occasional permissibility from establishing a regular fixed practice.