It wasnarrated that Ibn 'Umar said:
"I watched the Prophet (ﷺ) foramonth, and in the two Rak'ah before Fajr he used to recite: "Say:Oyou disbelievers!" [Al-Kafirun (109)] and "Say: Allah is One."[Al-Ikhlas (112)] (RU)
English reference (RU): Vol. 1, Book 5, Hadith 1149 (RU)
Arabic reference (RU): Book 5, Hadith 1203 (RU)