The Messenger of Allah ﷺ said, "Witr is a duty, so whoever does not pray witr is not one of us." He said it three times.
حدثنا الحسن بن يحيى حدثنا الفضل بن موسى عن عبيد الله العتكي
قال رسول الله ﷺ الوتر حق فمن لم يوتر فليس منا قالها ثلاثا
Its chain of transmission is hasan because of Ubaydullah al-Atki, who is Abu Munib Ubaydullah bin Abdullah, who has many errors. His hadith appears in the Sunan. This hadith has already appeared with similar wording at 22619.