The Prophet (ﷺ) said, "Night prayer is offered as two rak`at followed by two rak`at and so on, and if you want to finish it, pray only one rak`a which will be witr for all the previous rak`at." Al-Qasim said, "Since we attained the age of puberty we have seen some people offering a three-rak`at prayer as witr and all that is permissible. I hope there will be no harm in it."
Sahih al-Bukhari Book 14, Hadith 4
← Previous Hadith Once I passed the night in the house of Maimuna (his aunt). I slept across the bed while Allah's Apostle and his wife slept length-wise. The Prophet (ﷺ) slept till midnight or nearly so and woke up rubbing his face and recited ten verses from Surat "Al-`Imran." Allah's Messenger (ﷺ) went towards a leather skin and performed ablution in the most perfect way and then stood for the prayer. I did the same and stood beside him. The Prophet (ﷺ) put his right hand on my head, twisted my ear and then prayed two rak`at five times and then ended his prayer with witr. He laid down till the Mu'adh-dhin came then he stood up and offered two rak`at (Sunnah of Fajr prayer) and then went out and offered the Fajr prayer. (See Hadith 183)

Sahih al-Bukhari Book 14, Hadith 3 Next Hadith → Allah's Messenger (ﷺ) used to pray eleven rak`at at night and that was his night prayer and each of his prostrations lasted for a period enough for one of you to recite fifty verses before Allah's Messenger (ﷺ) raised his head. He also used to pray two rak`at (Sunnah) before the (compulsory) Fajr prayer and then lie down on his right side till the Mu'adh-dhin came to him for the prayer.

Sahih al-Bukhari Book 14, Hadith 5