The Prophet ﷺ said, "The night prayer is to be performed in pairs of two, and the witr is a single rakah at the end of the night."
حدثنا يزيد حدثنا هشام عن محمد
عن النبي ﷺ قال صلاة الليل مثنى مثنى والوتر ركعة من آخر الليل
Its isnad is sahih. Hisham is Ibn Hassan. Muhammad is Ibn Sirin. The hadith is a repetition of 4848. See 4860.