كتاب الصيام
13  
The Book of Fasting
(35)
Chapter: Prohibition of Fasting for a lifetime for the one who will be harmed by that or who will neglect other duties, or does not break his fast on the two 'Ids or during the days of At-Tashriq; It is better to fast alternate days
(35)
بَاب النَّهْيِ عَنْ صَوْمِ الدَّهْرِ لِمَنْ تَضَرَّرَ بِهِ أَوْ فَوَّتَ بِهِ حَقًّا أَوْ لَمْ يُفْطِرْ الْعِيدَيْنِ وَالتَّشْرِيقَ وَبَيَانِ تَفْضِيلِ صَوْمِ يَوْمٍ وَإِفْطَارِ يَوْمٍ
Sahih Muslim 1159 o

'Abdullah b. 'Amr (Allah be pleased with them) reported that the Messenger of Allah (ﷺ) said to me! 'Abdullah b. 'Amr, it has been conveyed to me that you observe fast during the day and stand in prayer during the whole night. Don't do that, for your body has a share of its own in you, your eye has a share of its own in you, your wife has a share of her own in you. Observe fast and break it too. Fast for three days in every month and that is a prepetual fasting. I said! Messenger of Allah, I have got strength enough (to do more than this), whereupon he said:

Then observe the fast of David (peace be upon him). Observe fast one day and break it (on the other) day. And he ('Abdullah b. 'Amr) used to say: Would that I had availed myself of this concession.
وَحَدَّثَنِي زُهَيْرُ بْنُ حَرْبٍ، وَمُحَمَّدُ بْنُ حَاتِمٍ، جَمِيعًا عَنِ ابْنِ مَهْدِيٍّ، - قَالَ زُهَيْرٌ حَدَّثَنَا عَبْدُ الرَّحْمَنِ بْنُ مَهْدِيٍّ، - حَدَّثَنَا سَلِيمُ بْنُ حَيَّانَ، حَدَّثَنَا سَعِيدُ بْنُ مِينَاءَ، قَالَ قَالَ عَبْدُ اللَّهِ بْنُ عَمْرٍو قَالَ لِي رَسُولُ اللَّهِ صلى الله عليه وسلم ‏"‏ يَا عَبْدَ اللَّهِ بْنَ عَمْرٍو بَلَغَنِي أَنَّكَ تَصُومُ النَّهَارَ وَتَقُومُ اللَّيْلَ فَلاَ تَفْعَلْ فَإِنَّ لِجَسَدِكَ عَلَيْكَ حَظًّا وَلِعَيْنِكَ عَلَيْكَ حَظًّا وَإِنَّ لِزَوْجِكَ عَلَيْكَ حَظًّا صُمْ وَأَفْطِرْ صُمْ مِنْ كُلِّ شَهْرٍ ثَلاَثَةَ أَيَّامٍ فَذَلِكَ صَوْمُ الدَّهْرِ ‏"‏ ‏.‏ قُلْتُ يَا رَسُولَ اللَّهِ إِنَّ بِي قُوَّةً ‏.‏ قَالَ ‏"‏ فَصُمْ صَوْمَ دَاوُدَ - عَلَيْهِ السَّلاَمُ - صُمْ يَوْمًا وَأَفْطِرْ يَوْمًا ‏"‏ ‏.‏ فَكَانَ يَقُولُ يَا لَيْتَنِي أَخَذْتُ بِالرُّخْصَةِ ‏.‏
Reference : Sahih Muslim 1159o
In-book reference : Book 13, Hadith 249
USC-MSA web (English) reference : Book 6, Hadith 2599
  (deprecated numbering scheme)