The Messenger of Allah ﷺ recited in the two units of Fajr "Say: O disbelievers" [Kafirun 109:1] and "Say: He is Allah, the One" [Ikhlas 112:1].
أن رسول الله ﷺ قرأ في ركعتي الفجر: {قل يأيها الكفرون} و {قل هو الله أحد}
Muslim narrated it in the Book of the Prayer of Travelers (726). He said, Muhammad bin Abbad and Ibn Abu Umar narrated to me, they said, Marwan bin Muawiya narrated to us, from Yazid (who is Ibn Kaysan), from Abu Hazim, from Abu Hurairah, and he related the hadith.What is intended here is the recitation in the two rakahs of the sunnah of Fajr.