The Messenger of Allah ﷺ used to recite in teh first rak'ah of Fajr "Say: We believe in Allah and that which has been sent down to us" to the end verse, and in the second rak'ah, "We believe in Allah, and bear witness that we are Muslims." (Using translation from Nasāʾī 944)  

أَخْبَرَهُ أَنَّ رَسُولَ اللهِ ﷺ كَانَ يَقْرَأُ فِي رَكْعَتَيِ الْفَجْرِ فِي الْأُولَى مِنْهُمَا الْآيَةَ الَّتِي فِي الْبَقَرَةِ {قُولُوا آمَنَّا بِاللهِ وَمَا أُنْزِلَ إِلَيْنَا} [البقرة 136] إِلَى آخِرِ الْآيَةِ وَفِي الْأُخْرَى {آمَنَّا بِاللهِ وَاشْهَدْ بِأَنَّا مُسْلِمُونَ} [آل عمران 52]