The Prophet ﷺ said, "The reciting of the Zabur (i.e. Psalms) was made easy for David. He used to order that his riding animals be saddled, and would finish reciting the Zabur before they were saddled. And he would never eat except from the earnings of his manual work."  

عَنِ النَّبِيِّ ﷺ قَالَ خُفِّفَ عَلَى دَاوُدَ عَلَيْهِ السَّلاَمُ الْقُرْآنُ فَكَانَ يَأْمُرُ بِدَوَابِّهِ فَتُسْرَجُ فَيَقْرَأُ الْقُرْآنَ قَبْلَ أَنْ تُسْرَجَ دَوَابُّهُ وَلاَ يَأْكُلُ إِلاَّ مِنْ عَمَلِ يَدِهِ رَوَاهُ مُوسَى بْنُ عُقْبَةَ عَنْ صَفْوَانَ عَنْ عَطَاءِ بْنِ يَسَارٍ عَنْ أَبِي هُرَيْرَةَ عَنِ النَّبِيِّ ﷺ  

Messenger of Allah ﷺ was informed that I have said: "By Allah, I will fast all the days and pray all the nights as long as I live." On that, Messenger of Allah ﷺ asked me. "Are you the one who says: 'I will fast all the days and pray all the nights as long as I live?' " I said, "Yes, I have said it." He said, "You cannot do that. So fast (sometimes) and do not fast (sometimes). Pray and sleep. Fast for three days a month, for the reward of a good deed is multiplied by ten time, and so the fasting of three days a month equals the fasting of a year." I said, "O Messenger of Allah ﷺ! I can do (fast) more than this." He said, "Fast on every third day. I said: I can do (fast) more than that, He said: "Fast on alternate days and this was the fasting of David which is the most moderate sort of fasting." I said, "O Messenger of Allah ﷺ! I can do (fast) more than that." He said, "There is nothing better than that."  

أُخْبِرَ رَسُولُ اللَّهِ ﷺ أَنِّي أَقُولُ وَاللَّهِ لأَصُومَنَّ النَّهَارَ وَلأَقُومَنَّ اللَّيْلَ مَا عِشْتُ فَقَالَ لَهُ رَسُولُ اللَّهِ ﷺ أَنْتَ الَّذِي تَقُولُ وَاللَّهِ لأَصُومَنَّ النَّهَارَ وَلأَقُومَنَّ اللَّيْلَ مَا عِشْتُ قُلْتُ قَدْ قُلْتُهُ قَالَ إِنَّكَ لاَ تَسْتَطِيعُ ذَلِكَ فَصُمْ وَأَفْطِرْ وَقُمْ وَنَمْ وَصُمْ مِنَ الشَّهْرِ ثَلاَثَةَ أَيَّامٍ فَإِنَّ الْحَسَنَةَ بِعَشْرِ أَمْثَالِهَا وَذَلِكَ مِثْلُ صِيَامِ الدَّهْرِ فَقُلْتُ إِنِّي أُطِيقُ أَفْضَلَ مِنْ ذَلِكَ يَا رَسُولَ اللَّهِ قَالَ فَصُمْ يَوْمًا وَأَفْطِرْ يَوْمَيْنِ قَالَ قُلْتُ إِنِّي أُطِيقُ أَفْضَلَ مِنْ ذَلِكَ قَالَ فَصُمْ يَوْمًا وَأَفْطِرْ يَوْمًا وَذَلِكَ صِيَامُ دَاوُدَ وَهْوَ عَدْلُ الصِّيَامِ قُلْتُ إِنِّي أُطِيقُ أَفْضَلَ مِنْهُ يَا رَسُولَ اللَّهِ قَالَ لاَ أَفْضَلَ مِنْ ذَلِكَ  

The Prophet ﷺ said to me, "I have been informed that you pray all the nights and observe fast all the days; is this true?" I replied, "Yes." He said, "If you do so, your eyes will become weak and you will get bored. So fast three days a month, for this will be the fasting of a whole year, or equal to the fasting of a whole year." I said, "I find myself able to fast more." He said, "Then fast like the fasting of (the Prophet) David who used to fast on alternate days and would not flee on facing the enemy."  

لِي رَسُولُ اللَّهِ ﷺ أَلَمْ أُنَبَّأْ أَنَّكَ تَقُومُ اللَّيْلَ وَتَصُومُ فَقُلْتُ نَعَمْ فَقَالَ فَإِنَّكَ إِذَا فَعَلْتَ ذَلِكَ هَجَمَتِ الْعَيْنُ وَنَفِهَتِ النَّفْسُ صُمْ مِنْ كُلِّ شَهْرٍ ثَلاَثَةَ أَيَّامٍ فَذَلِكَ صَوْمُ الدَّهْرِ أَوْ كَصَوْمِ الدَّهْرِ قُلْتُ إِنِّي أَجِدُ بِي قَالَ مِسْعَرٌ يَعْنِي قُوَّةً قَالَ فَصُمْ صَوْمَ دَاوُدَ عَلَيْهِ السَّلاَمُ وَكَانَ يَصُومُ يَوْمًا وَيُفْطِرُ يَوْمًا وَلاَ يَفِرُّ إِذَا لاَقَى