The Prophet ﷺ said, "The witr is the final rakah of the night prayer."
حدثنا محمد بن جعفر وحجاج قالا حدثنا شعبة عن أبي التياح عن أبي مجلز
عن النبي ﷺ قال الوتر آخر ركعة من الليل
Its isnad is sahih. Abu Tayah is Yazid bin Humayd, whose reliability was established earlier at 689, and we add here that Bukhari gave his biography in Kabir 4/2/326. The hadith is an abridged version of 4878.