The Prophet ﷺ would recite in the two (supererogatory) rak'ahs of the dawn prayer: "Say, O unbelievers" [Surat al-Kafiroon:1] and "Say: He is Allah, the one" [Surat al-Ikhlas:1] (Using translation from Abū Dāʾūd 1256)

أَسَرَّ تَعْنِي النَّبِيَّ ﷺ الْقِرَاءَةَ فِي رَكْعَتَيِ الْفَجْرِ وَقَرَأَ فِيهِمَا قُلْ يَا أَيُّهَا الْكَافِرُونَ وَقُلْ هُوَ اللهُ أَحَدٌ