Witr is a rak'ah at the end of the prayer.
Sahih Muslim Book 6, Hadith 186
← Previous Hadith He who observed the night prayer should make Witr the end of his prayer before dawn. The Messenger of Allah (ﷺ) used to order them thus.

Sahih Muslim Book 6, Hadith 185 Next Hadith → Witr is a rak'ah at the end of the night prayer.

Sahih Muslim Book 6, Hadith 187