Abu Hurairah (RA) reported that the Messenger of Allah (ﷺ) recited in the two (supererogatory) rak'ahs of the dawn (prayer): "Say: O unbelievers," (Qur'an, cix.) and "Say: Allah is one" (cxii.).
Hadith ReferenceSahih Muslim / The Book of Prayer - Travellers / Hadith: 726