´It was narrated from Abu Hurairah that in the two Rak’ah before the Fajr, the Prophet (ﷺ) used to recite:` “Say: ‘O you disbelievers!” [Al-Kafirun (109)] and “Say: Allah is One.” [Al-Ikhlas (112)]
Hadith Referenceسنن ابن ماجه / كتاب إقامة الصلاة والسنة / 1148
Hadith Gradingالألبانی:صحيح | زبیر علی زئی:صحيح مسلم
Narrated Abu Hurairah: The Prophet ﷺ would recite in both rak'ahs of the dawn prayer: "Say, O unbelievers" and "Say: He is Allah, the one"
Shaykh Umar Farooq Saeedi
1256. Commentary: The choice and adherence to this recitation is recommended (mustahabb), and from a semantic perspective, it holds special significance in that, at the very beginning of the day, a Muslim declares his disavowal from disbelief and disbelievers, and affirms and acknowledges the oneness (tawhid) of Allah, the Mighty and Majestic, as well as His names and attributes. Furthermore, mention of other recitations will come ahead.
Source: Sunan Abu Dawood – Commentary by Shaykh Umar Farooq Saeedi, Page: 1256