Narrated 'Abdullah bin Amr bin Al-As:

My father got me married to a lady of a noble family, and often used to ask my wife about me, and she used to reply, "What a wonderful man he is! He never comes to my bed, nor has he approached me since he married me." When this state continued for a long period, my father told the story to the Prophet who said to my father, "Let me meet him." Then I met him and he asked me, "How do you fast?" I replied, "I fast daily," He asked, "How long does it take you to finish the recitation of the whole Quran?" I replied, "I finish it every night." On that he said, "Fast for three days every month and recite the Qur'an (and finish it) in one month." I said, "But I have power to do more than that." He said, "Then fast for three days per week." I said, "i have the power to do more than that." He said, "Therefore, fast the most superior type of fasting, (that is, the fasting of (prophet) David who used to fast every alternate day;
and finish the recitation of the whole Qur'an In seven days." I wish I had accepted the permission of Allah's Apostle as I have become a weak old man. It is said that 'Abdullah used to recite one-seventh of the Qur'an during the day-time to some of his family members, for he used to check his memorization of what he would recite at night during the daytime so that it would be easier for him to read at night. And whenever he wanted to gain some strength, he used to give up fasting for some days and count those days to fast for a similar period, for he disliked to leave those things which he used to do during the lifetime of the Prophet.

حَدَّثَنَا مُوسَى، حَدَّثَنَا أَبُو عَوَانَةَ، عَنْ مُغِيرَةَ، عَنْ مُجَاهِدٍ، عَنْ عَبْدِ اللَّهِ بْنِ عَمْرٍو، قَالَ أَنْكَحَنِي أَبِي امْرَأَةً ذَاتَ حَسَبٍ فَكَانَ يَتَعَاهَدُ كَنَّتَهُ فَيَسْأَلُهَا عَنْ بَعْلِهَا فَتَقُولُ نِعْمَ الرَّجُلُ مِنْ رَجُلٍ لَمْ يَطَأْ لَنَا فِرَاشًا وَلَمْ يُفَتِّشْ لَنَا كَنَفًا مُذْ أَتَيْنَاهُ فَلَمَّا طَالَ ذَلِكَ عَلَيْهِ ذَكَرَ لِلنَّبِيِّ ﷺ فَقَالَ " الْقَنِي بِهِ ". فَلَقِيتُهُ بَعْدُ فَقَالَ " كَيْفَ تَصُومُ ". قَالَ كُلَّ يَوْمٍ. قَالَ " وَكَيْفَ تَخْتِمُ ". قَالَ كُلَّ لَيْلَةً. قَالَ " صُمْ فِي كُلِّ شَهْرٍ ثَلاَثَةً وَاقْرَإِ الْقُرْآنَ فِي كُلِّ شَهْرٍ ". قَالَ قُلْتُ أُطِيقُ أَكْثَرَ مِنْ ذَلِكَ. قَالَ " صُمْ ثَلاَثَةَ أَيَّامٍ فِي الْجُمُعَةِ ". قُلْتُ أُطِيقُ أَكْثَرَ مِنْ ذَلِكَ. قَالَ " أَفْطِرْ يَوْمَيْنِ وَصُمْ يَوْمًا ". قَالَ قُلْتُ أُطِيقُ أَكْثَرَ مِنْ ذَلِكَ. قَالَ " صُمْ أَفْضَلَ الصَّوْمِ صَوْمِ دَاوُدَ صِيَامَ يَوْمٍ وَإِفْطَارَ يَوْمٍ وَاقْرَأْ فِي كُلِّ سَبْعِ لَيَالٍ مَرَّةً ". فَلَيْتَنِي قَبِلْتُ رُخْصَةَ رَسُولِ اللَّهِ ﷺ وَذَاكَ أَنِّي كَبِرْتُ وَضَعُفْتُ فَكَانَ يَقْرَأُ عَلَى بَعْضِ أَهْلِهِ السُّبْعَ مِنَ الْقُرْآنِ بِالنَّهَارِ وَالَّذِي يَقْرَؤُهُ يَعْرِضُهُ مِنَ النَّهَارِ لِيَكُونَ أَخَفَّ عَلَيْهِ بِاللَّيْلِ وَإِذَا أَرَادَ أَنْ يَتَقَوَّى أَفْطَرَ أَيَّامًا وَأَحْصَى وَصَامَ مِثْلَهُنَّ كَرَاهِيةَ أَنْ يَتْرُكَ شَيْئًا فَارَقَ النَّبِيَّ ﷺ عَلَيْهِ. قَالَ أَبُو عَبْدِ اللَّهِ وَقَالَ بَعْضُهُمْ فِي ثَلاَثٍ وَفِي خَمْسٍ وَأَكْثَرُهُمْ عَلَى سَبْعٍ.