Offer Fajr prayer at dawn, for it is most productive of rewards to you or most productive of reward.

قَالَ رَسُولُ اللَّهِ ﷺ أَصْبِحُوا بِالصُّبْحِ فَإِنَّهُ أَعْظَمُ لأُجُورِكُمْ أَوْ أَعْظَمُ لِلأَجْرِ