The Prophet ﷺ, when dawn broke for him, would pray two rakahs.
حدثنا هشام بن عمار حدثنا سفيان بن عيينة عن عمرو بن دينار
أن النبي ﷺ كان إذا أضاء له الفجر صلى ركعتين
No references are available.
[Sahih] * Sufyan bin Uyayna narrated with "an" phrasing, but it has a corroborating narration in Muslim, no. 723, from the hadith of Sufyan bin Uyayna, from Amr bin Dinar, from Zuhri, from Salim, from his father, from Hafsa.