The Messenger of Allah ﷺ used to pray two units of prayer before the dawn prayer, and he would say, "What excellent two surahs they are to recite in the two units before Fajr, Say, He is Allah, the One and Say, O you disbelievers."
حدثنا أبو بكر بن أبي شيبة حدثنا يزيد بن هارون حدثنا الجريري عن عبد الله بن شقيق
كان رسول الله ﷺ يصلي ركعتين قبل الفجر وكان يقول نعم السورتان هما يقرأ بهما في ركعتي الفجر قل هو الله أحد وقل يا أيها الكافرون
Its chain is daif. Ahmad narrated it (6/239) from Yazid, and Ibn Hibban graded it sahih (no. 610), as did Ibn Khuzayma (no. 1114), from the hadith of Ishaq bin Yusuf Azraq from Jareeri. Hafiz strengthened it in Fath al-Bari (3/47).Jareeri's memory became confused, and the hearing of Yazid bin Harun and Ishaq Azraq from him was after his confusion set in, as stated in Taqyeed wal-Idah, p. 427. The hadith has corroborating narrations.