The Messenger of Allah ﷺ said, "The night prayer is to be performed in pairs of two. When you fear the approach of dawn, pray a single rakah as witr."
حدثنا عبد الرزاق حدثنا معمر عن الزهري عن سالم
قال رسول الله ﷺ صلاة الليل مثنى مثنى فإذا خفت الصبح فأوتر بواحدة
Its isnad is sahih. It is an abridgment of 6176 and 6258, and see also 6300.