"I would see the Messenger of Allah ﷺ praying two rak'ahs of Fajr and making them so brief that I said: 'Did he recite the Umm Al-Kitab in them?'"  

إِنْ كُنْتُ لأَرَى رَسُولَ اللَّهِ ﷺ يُصَلِّي رَكْعَتَىِ الْفَجْرِ فَيُخَفِّفُهُمَا حَتَّى أَقُولَ أَقَرَأَ فِيهِمَا بِأُمِّ الْكِتَابِ