The Prophet ﷺ said, "Whoever reaches the dawn without having prayed witr, there is no witr for him."
أن النبي ﷺ قال: من أدرك الصبح فلم يوتر، فلا وثر له.
No references are available.
Ibn Khuzayma (1092), Ibn Hibban (2408), and Hakim (1/301-302) all narrated it through Hisham, from Qatada, from Abu Nadra, from Abu Saeed, and he mentioned it. Hakim graded it sahih according to the criterion of Muslim.