The Messenger of Allah (ﷺ) recited: "Say: O you disbelievers" and "Say: He is Allah, (the) One" in the two rak'ahs of Fajr.
Sunan an-Nasa'i Book 11, Hadith 70
← Previous Hadith The Messenger of Allah (ﷺ) used to recite in teh first rak'ah of Fajr "Say: We believe in Allah and that which has been sent down to us" to the end verse, and in the second rak'ah, "We believe in Allah, and bear witness that we are Muslims."

Sunan an-Nasa'i Book 11, Hadith 69 Next Hadith → "I would see the Messenger of Allah (ﷺ) praying two rak'ahs of Fajr and making them so brief that I said: 'Did he recite the Umm Al-Kitab in them?'"

Sunan an-Nasa'i Book 11, Hadith 71