The Prophet ﷺ said to me, "You fast daily all the year and pray every night all the night?" I replied in the affirmative. The Prophet ﷺ said, "If you keep on doing this, your eyes will become weak and your body will get tired. He who fasts all the year is as he who did not fast at all. The fasting of three days (a month) will be equal to the fasting of the whole year." I replied, "I have the power for more than this." The Prophet ﷺ said, "Then fast like the fasting of David who used to fast on alternate days and would never flee from the battle field, on meeting the enemy." (Using translation from Bukhārī 1979)
سَمِعْتُ أَبَا الْعَبَّاسِ الْمَكِّيَّ وَكَانَ شَاعِرًا وَكَانَ لَا يُتَّهَمُ فِي الْحَدِيثِ قَالَ سَمِعْتُ عَبْدَ اللهِ بْنَ عَمْرِو بْنِ الْعَاصِ يَقُولُ قَالَ لِي رَسُولُ اللهِ ﷺ إِنَّكَ تَصُومُ الدَّهْرَ وَتَقُومُ اللَّيْلَ قُلْتُ نَعَمْ قَالَ إِنَّكَ إِذَا فَعَلْتَ ذَلِكَ هَجَمَتْ لَهُ الْعَيْنُ وَنَفِهَتْ لَهُ النَّفْسُ لَا صَامَ مَنْ صَامَ الدَّهْرَ صُمْ ثَلَاثَةَ أَيَّامٍ مِنَ الشَّهْرِ صَوْمُ الدَّهْرِ كُلِّهِ قَالَ فَقُلْتُ فَإِنِّي أُطِيقُ أَكْثَرَ مِنْ ذَلِكَ قَالَ فَصُمْ صَوْمَ دَاوُدَ كَانَ يَصُومُ يَوْمًا وَيُفْطِرُ يَوْمًا وَلَا يَفِرُّ إِذَا لَاقَى