It was narrated that Ibn Al-Malih said:

"I entered with Zaid upon 'Abdullah bin Amr and he narrated: 'The Messenger of Allah was told about my fasting, so the entered upon me and I gave him an average-sized leather pillow that was stuffed with palm fibvers. He sat in the ground with the pillow between myself and him, and said: "Whill it not be sufficient for you to fast three days each months?" I said: O Messenger of Allah! He said: "O Messenger of Allah!" He said: "Eleven." I said: "O Messenger of Allah!" Then the Prophet ﷺ said: "There is not fast better than the fast of Dawud, half of a lifetime, fasting one day and not next."

أَخْبَرَنَا زَكَرِيَّاءُ بْنُ يَحْيَى، قَالَ حَدَّثَنَا وَهْبُ بْنُ بَقِيَّةَ، قَالَ أَنْبَأَنَا خَالِدٌ، عَنْ خَالِدٍ، - وَهُوَ الْحَذَّاءُ - عَنْ أَبِي قِلاَبَةَ، عَنْ أَبِي الْمَلِيحِ، قَالَ دَخَلْتُ مَعَ أَبِيكَ زَيْدٍ عَلَى عَبْدِ اللَّهِ بْنِ عَمْرٍو فَحَدَّثَ أَنَّ رَسُولَ اللَّهِ ﷺ ذُكِرَ لَهُ صَوْمِي فَدَخَلَ عَلَىَّ فَأَلْقَيْتُ لَهُ وِسَادَةَ أَدَمٍ رَبْعَةً حَشْوُهَا لِيفٌ فَجَلَسَ عَلَى الأَرْضِ وَصَارَتِ الْوِسَادَةُ فِيمَا بَيْنِي وَبَيْنَهُ قَالَ " 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 . فَقَالَ النَّبِيُّ ﷺ " لاَ صَوْمَ فَوْقَ صَوْمِ دَاوُدَ شَطْرَ الدَّهْرِ صِيَامُ يَوْمٍ وَفِطْرُ يَوْمٍ " .