Sahih Bukhari Volume 8, Book 79, Hadith 6279

حَدَّثَنَا إِسْحَاقُ، حَدَّثَنَا خَالِدٌ،‏.‏ وَحَدَّثَنِي عَبْدُ اللَّهِ بْنُ مُحَمَّدٍ، حَدَّثَنَا عَمْرُو بْنُ عَوْنٍ، حَدَّثَنَا خَالِدٌ، عَنْ خَالِدٍ، عَنْ أَبِي قِلاَبَةَ، قَالَ أَخْبَرَنِي أَبُو الْمَلِيحِ، قَالَ دَخَلْتُ مَعَ أَبِيكَ زَيْدٍ عَلَى عَبْدِ اللَّهِ بْنِ عَمْرٍو فَحَدَّثَنَا أَنَّ النَّبِيَّ صلى الله عليه وسلم ذُكِرَ لَهُ صَوْمِي، فَدَخَلَ عَلَىَّ، فَأَلْقَيْتُ لَهُ وِسَادَةً مِنْ أَدَمٍ حَشْوُهَا لِيفٌ، فَجَلَسَ عَلَى الأَرْضِ، وَصَارَتِ الْوِسَادَةُ بَيْنِي وَبَيْنَهُ، فَقَالَ لِي ‏"‏ أَمَا يَكْفِيكَ مِنْ كُلِّ شَهْرٍ ثَلاَثَةُ أَيَّامٍ ‏"‏‏.‏ قُلْتُ يَا رَسُولَ اللَّهِ‏.‏ قَالَ ‏"‏ خَمْسًا ‏"‏‏.‏ قُلْتُ يَا رَسُولَ اللَّهِ‏.‏ قَالَ ‏"‏ سَبْعًا ‏"‏‏.‏ قُلْتُ يَا رَسُولَ اللَّهِ‏.‏ قَالَ ‏"‏ تِسْعًا ‏"‏‏.‏ قُلْتُ يَا رَسُولَ اللَّهِ‏.‏ قَالَ ‏"‏ إِحْدَى عَشْرَةَ ‏"‏‏.‏ قُلْتُ يَا رَسُولَ اللَّهِ‏.‏ قَالَ ‏"‏ لاَ صَوْمَ فَوْقَ صَوْمِ دَاوُدَ، شَطْرَ الدَّهْرِ، صِيَامُ يَوْمٍ، وَإِفْطَارُ يَوْمٍ ‏"‏‏.

Narrated By Abdullah bin 'Amr : The news of my fasting was mentioned to the Prophet. So he entered upon me and I put for him a leather cushion stuffed with palm-fibres. The Prophet sat on the floor and the cushion was between me and him. He said to me, "Isn't it sufficient for you (that you fast) three days a month?" I said, "O Allah's Apostle! (I can fast more than this)." He said, "You may fast) five days a month." I said, "O Allah's Apostle! (I can fast more than this)." He said, "(You may fast) seven days." I said, "O Allah's Apostle!" He said, "Nine." I said, "O Allah's Apostle!" He said, "Eleven." I said, "O Allah's Apostle!" He said, "No fasting is superior to the fasting of (the Prophet David) which was one half of a year, and he used, to fast on alternate days.