The Messenger of Allah ﷺ said, "Pray witr before morning comes."
حدثنا عبد الرزاق حدثنا معمر عن يحيى بن أبي كثير عن أبي نضرة
قال رسول الله ﷺ أوتروا قبل أن تصبحوا
No references are available.
Its chain of transmission is sahih. The hadith has already appeared at 11039, and its wording there is according to Muslim.