It wasnarrated that 'Aishah said:
"The Messenger of Allah (ﷺ) usedtoperform two Rak'ah before Fajr, and he used to say: 'The best twoSurah to recite in the two Rak'ah of Fajr are: "Say: Allah isOne"[Al-Ikhlas (112)] and "Say: O you disbelievers."[Al-Kafirun (109)] (DE)
English reference (DE): Vol. 1, Book 5, Hadith 1150 (DE)
Arabic reference (DE): Book 5, Hadith 1204 (DE)