"The Messenger of Allah ﷺ used to pray Zuhr when the sun passed its zenith, and he would pray 'Asr between these two prayers; and he would pray Maghrib when the sun had set, and he used to pray 'Isha' when the twilight had disappeared," then he said straight after that: "And he would pray Fajr when a man could see clearly."  

كَانَ رَسُولُ اللَّهِ ﷺ يُصَلِّي الظُّهْرَ إِذَا زَالَتِ الشَّمْسُ وَيُصَلِّي الْعَصْرَ بَيْنَ صَلاَتَيْكُمْ هَاتَيْنِ وَيُصَلِّي الْمَغْرِبَ إِذَا غَرَبَتِ الشَّمْسُ وَيُصَلِّي الْعِشَاءَ إِذَا غَابَ الشَّفَقُ ثُمَّ قَالَ عَلَى إِثْرِهِ وَيُصَلِّي الصُّبْحَ إِلَى أَنْ يَنْفَسِحَ الْبَصَرُ