It was narrated from 'Abdullah bin 'Amr bin Al-As that it was mentioned to the Messenger of Allah that he had said:

"I will certainly stand all night (in prayer) and fast every day for as long as I live." The Messenger of Allah said: "Are you the one who said that?" I said: 'I said it, O Messenger of Allah.' The Messenger of Allah said: 'You cannot do that. Fast and break your fast, sleep and stand (in prayer), and fast three days of each month. For a good deed is equal to ten like it, and that is like fasting for a lifetime.' I said: 'But I am able to do bette than that.' He said: 'Fast for one day and break your fast for two days.' I said: 'I am able to do better than that, O Messenger of Allah.' He said: 'Then fast for one day and break your fast for two days.' I said: 'I am able to do better than that, O Messenger of Allah said : 'There is noting better than that."' 'Abdullah said: "If I had accepted the three days that the Messenger of Allah said, that would be dearer to me than my family and my wealth." 'Ata said: "someone who heard him told me that Ibn 'Umar (said) that the Prophet ﷺ said: 'Whoever fasts every day of his life, then he has not fasted."

أَخْبَرَنَا الرَّبِيعُ بْنُ سُلَيْمَانَ، قَالَ حَدَّثَنَا ابْنُ وَهْبٍ، قَالَ أَخْبَرَنِي يُونُسُ، عَنِ ابْنِ شِهَابٍ، قَالَ أَخْبَرَنِي سَعِيدُ بْنُ الْمُسَيَّبِ، وَأَبُو سَلَمَةَ بْنُ عَبْدِ الرَّحْمَنِ أَنَّ عَبْدَ اللَّهِ بْنَ عَمْرِو بْنِ الْعَاصِ، قَالَ ذُكِرَ لِرَسُولِ اللَّهِ ﷺ أَنَّهُ يَقُولُ لأَقُومَنَّ اللَّيْلَ وَلأَصُومَنَّ النَّهَارَ مَا عِشْتُ . فَقَالَ رَسُولُ اللَّهِ ﷺ " أَنْتَ الَّذِي تَقُولُ ذَلِكَ " . فَقُلْتُ لَهُ قَدْ قُلْتُهُ يَا رَسُولَ اللَّهِ . فَقَالَ رَسُولُ اللَّهِ ﷺ " فَإِنَّكَ لاَ تَسْتَطِيعُ ذَلِكَ فَصُمْ وَأَفْطِرْ وَنَمْ وَقُمْ وَصُمْ مِنَ الشَّهْرِ ثَلاَثَةَ أَيَّامٍ فَإِنَّ الْحَسَنَةَ بِعَشْرِ أَمْثَالِهَا وَذَلِكَ مِثْلُ صِيَامِ الدَّهْرِ " . قُلْتُ فَإِنِّي أُطِيقُ أَفْضَلَ مِنْ ذَلِكَ . قَالَ " صُمْ يَوْمًا وَأَفْطِرْ يَوْمَيْنِ " . فَقُلْتُ إِنِّي أُطِيقُ أَفْضَلَ مِنْ ذَلِكَ يَا رَسُولَ اللَّهِ . قَالَ " فَصُمْ يَوْمًا وَأَفْطِرْ يَوْمًا وَذَلِكَ صِيَامُ دَاوُدَ وَهُوَ أَعْدَلُ الصِّيَامِ " . قُلْتُ فَإِنِّي أُطِيقُ أَفْضَلَ مِنْ ذَلِكَ . قَالَ رَسُولُ اللَّهِ ﷺ " لاَ أَفْضَلَ مِنْ ذَلِكَ " . قَالَ عَبْدُ اللَّهِ بْنُ عَمْرٍو لأَنْ أَكُونَ قَبِلْتُ الثَّلاَثَةَ الأَيَّامَ الَّتِي قَالَ رَسُولُ اللَّهِ ﷺ أَحَبُّ إِلَىَّ مِنْ أَهْلِي وَمَالِي .