حَدَّثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، حَدَّثَنَا اللَّيْثُ، عَنِ ابْنِ شِهَابٍ، عَنْ أَنَسِ بْنِ مَالِكٍ، أَنَّهُ أَخْبَرَهُ أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم كَانَ يُصَلِّي الْعَصْرَ وَالشَّمْسُ بَيْضَاءُ مُرْتَفِعَةٌ حَيَّةٌ وَيَذْهَبُ الذَّاهِبُ إِلَى الْعَوَالِي وَالشَّمْسُ مُرْتَفِعَةٌ ‏.‏

Abu Hurairah reported the Messenger of Allah (ﷺ) as saying

If anyone says a rak'ah of the 'Asr prayer before sunset, he has observed (the 'Asr prayer), and if anyone performs a rak'ah of the Fajr prayer, he has observed (the Fajr prayer).