Sayyiduna Ubayy bin Ka'b (may Allah be pleased with him) said that the Prophet (peace and blessings be upon him) "used to recite in witr 'Glorify the name of your Lord, the Most High' [Surah al-A'la: 1], 'Say: O disbelievers' [Surah al-Kafirun: 1] and 'Say: He is Allah, the One' [Surah al-Ikhlas: 1]."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4856