Sahih Muslim Book - 13, Hadith - 2736

وَحَدَّثَنَا عُبَيْدُ اللَّهِ بْنُ مُعَاذٍ حَدَّثَنِى أَبِى حَدَّثَنَا شُعْبَةُ عَنْ حَبِيبٍ سَمِعَ أَبَا الْعَبَّاسِ سَمِعَ عَبْدَ اللَّهِ بْنَ عَمْرٍو - رضى الله عنهما - قَالَ قَالَ لِى رَسُولُ اللَّهِ -صلى الله عليه وسلم- « يَا عَبْدَ اللَّهِ بْنَ عَمْرٍو إِنَّكَ لَتَصُومُ الدَّهْرَ وَتَقُومُ اللَّيْلَ وَإِنَّكَ إِذَا فَعَلْتَ ذَلِكَ هَجَمَتْ لَهُ الْعَيْنُ وَنَهِكَتْ لاَ صَامَ مَنْ صَامَ الأَبَدَ صَوْمُ ثَلاَثَةِ أَيَّامٍ مِنَ الشَّهْرِ صَوْمُ الشَّهْرِ كُلِّهِ ». قُلْتُ فَإِنِّى أُطِيقُ أَكْثَرَ مِنْ ذَلِكَ. قَالَ « فَصُمْ صَوْمَ دَاوُدَ كَانَ يَصُومُ يَوْمًا وَيُفْطِرُ يَوْمًا وَلاَ يَفِرُّ إِذَا لاَقَى ».

‘Abdullah bin ‘Amr [may Allah be pleased with them] said: “The Messenger of Allah (SAW) said to me: ‘O ‘Abdullah bin ‘Amr, you fast all the time and spend your nights in prayer, but if you do that, your eyes will become sunken and will become weak. He has not fasted who fasts all the time. Fasting for three days of every month is like fasting for the entire month.’ I said: I am able to do more than that.’ He said: ‘Then observe the fast of Dawud, for he used to fast one day and not the next, and he would not flee if he encountered (an enemy).”’