Amrah (may Allah have mercy on her) narrates from Sayyidah Aishah (may Allah be pleased with her) that the Messenger of Allah (peace and blessings be upon him) used to recite, in the two rak'ahs after which he would pray witr, "Glorify the name of your Lord, the Most High" [Surah al-A'la: 1] and "Say: O disbelievers" [Surah al-Kafirun: 1], and in the witr "Say: He is Allah, the One" [Surah al-Ikhlas: 1], "Say: I seek refuge with the Lord of the daybreak" [Surah al-Falaq: 1] and "Say: I seek refuge with the Lord of mankind" [Surah al-Nas: 1].
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4852