The Messenger of Allah ﷺ used to pray the two rakahs of Fajr as soon as he heard the call to prayer, performing them briefly.
كان رسول الله ﷺ يصلي ركعتي الفجر إذا سمع الأذان، يخففهما.
Muslim narrated it in "Prayer of the Traveler" (724), from Amr al-Naqid, from Abdah bin Sulayman, from Hisham bin Urwa, from his father, from Ayesha.In another narration, "when Fajr rises."In another narration, "He used to pray two units of prayer between the call and the standing call to the dawn prayer."