When dawn broke, the Messenger of Allah ﷺ would pray only two rakahs, and I would say that he recited in them the Opening of the Book.
حدثنا يحيى عن شعبة عن محمد بن عبد الرحمن بن أسعد بن زرارة عن عروة
كان رسول الله ﷺ إذا طلع الفجر لا يصلي إلا ركعتين فأقول قرأ فيهما بفاتحة الكتاب
Its isnad is sahih. Muhammad bin Abdul-Rahman bin Asad, the correct form being Saad, bin Zurara, is trustworthy, and his hadith is found in the six major collections. The hadith was narrated by Bukhari 3/46 no. 1171 in the Book of Prayer, Muslim 1/500 no. 724 in the Book of Travelers, Abu Dawud 2/19 no. 1255, all of them in the Book of Prayer, and Nasai 2/156 no. 946 in the Book of Opening (the Prayer).