Sunan an-Nasa'i 2393
It was narrated that Abu Salamah bin 'Abdur-Rahman said:
"I entered upon 'Abdullah bin 'Amr and said: O uncle, tell me what the Messenger of Allah said to you. He said: O son of my brother, I had resolved to strive very hard until I said: I will fast for the rest of my life and I will read the whole Quran every day and night. The Messenger of Allah heard about that, and came in to me in my house, and said: I have heard that you said, I will fast for a lifetime and will read the Quran. I said: I did say that, O Messenger of Allah. He said; Do not do that. Fast three days of each month. I said: I am able to do more than that. He said: fast two days of each week, Monday and Thursday. I said: I am able to do more than that. He said; Observe the fast of Dawud, peace be upon him, for it is the best kind of fasting before Allah; one day fasting, and one day not fasting. And when he made a promise he did not break it, and when he met (the enemy in battle) he did not flee." 'Ata said: "someone who heard him told me that Ibn 'Umar (said) that the Prophet said: 'Whoever fasts every day of his life, then he has not fasted."
أَخْبَرَنِي أَحْمَدُ بْنُ بَكَّارٍ، قَالَ حَدَّثَنَا مُحَمَّدٌ، - وَهُوَ ابْنُ سَلَمَةَ - عَنِ ابْنِ إِسْحَاقَ، عَنْ مُحَمَّدِ بْنِ إِبْرَاهِيمَ، عَنْ أَبِي سَلَمَةَ بْنِ عَبْدِ الرَّحْمَنِ، قَالَ دَخَلْتُ عَلَى عَبْدِ اللَّهِ بْنِ عَمْرٍو قُلْتُ أَىْ عَمِّ حَدِّثْنِي عَمَّا قَالَ لَكَ رَسُولُ اللَّهِ صلى الله عليه وسلم قَالَ يَا ابْنَ أَخِي إِنِّي كُنْتُ أَجْمَعْتُ عَلَى أَنْ أَجْتَهِدَ اجْتِهَادًا شَدِيدًا حَتَّى قُلْتُ لأَصُومَنَّ الدَّهْرَ وَلأَقْرَأَنَّ الْقُرْآنَ فِي كُلِّ يَوْمٍ وَلَيْلَةٍ فَسَمِعَ بِذَلِكَ رَسُولُ اللَّهِ صلى الله عليه وسلم فَأَتَانِي حَتَّى دَخَلَ عَلَىَّ فِي دَارِي فَقَالَ ‏"‏ بَلَغَنِي أَنَّكَ قُلْتَ لأَصُومَنَّ الدَّهْرَ وَلأَقْرَأَنَّ الْقُرْآنَ ‏"‏ ‏.‏ فَقُلْتُ قَدْ قُلْتُ ذَلِكَ يَا رَسُولَ اللَّهِ ‏.‏ قَالَ ‏"‏ فَلاَ تَفْعَلْ صُمْ مِنْ كُلِّ شَهْرٍ ثَلاَثَةَ أَيَّامٍ ‏"‏ ‏.‏ قُلْتُ إِنِّي أَقْوَى عَلَى أَكْثَرَ مِنْ ذَلِكَ ‏.‏ قَالَ ‏"‏ فَصُمْ مِنَ الْجُمُعَةِ يَوْمَيْنِ الاِثْنَيْنِ وَالْخَمِيسَ ‏"‏ ‏.‏ قُلْتُ فَإِنِّي أَقْوَى عَلَى أَكْثَرَ مِنْ ذَلِكَ ‏.‏ قَالَ ‏"‏ فَصُمْ صِيَامَ دَاوُدَ عَلَيْهِ السَّلاَمُ فَإِنَّهُ أَعْدَلُ الصِّيَامِ عِنْدَ اللَّهِ يَوْمًا صَائِمًا وَيَوْمًا مُفْطِرًا وَإِنَّهُ كَانَ إِذَا وَعَدَ لَمْ يُخْلِفْ وَإِذَا لاَقَى لَمْ يَفِرَّ ‏"‏ ‏.‏