بسم الله الرحمن الرحيم

He ﷺ if he performed witr as 3 used to recite Surah al-‘Ala in the first unit of prayer (after al-Fatihah) because this soorah consists of mention of the worldly life and the Hereafter. In the second rak’ah he recites Surah Al-Kaafiroon because it consists of Tawheed of Worship, Tawheed al-Uloohiyah, and in the third he recites Surah Al-Ikhlaas.

Shaykh Fawzan’s Tasheel al-Almaam Sharh Buloogh al-Maraam Vol.2 Pg. 361