Observe fast for a day and there would be reward for you for the rest (of the days). He said: I am capable of doing more than this. He then said: Observe fast for two days, and there would be reward for you for the rest (of the days). He said: I am capable of doing more than this. He (the Holy Prophet) said: Observe fast for three days and there would be reward for you for the rest of the days. He said: I am capable of doing more than this, whereupon he said: Observe fast for four days and there would be reward for you for the rest of the days. He said: I am capable of doing more than this. Thereupon he said: Then observe fast (which is the) best in the eye of Allah, the fast of David (peace be upon him) ; he used to observe fast one day and break on the other day. (Using translation from Muslim 1159n)  

أَنَّ رَسُولَ اللهِ ﷺ قَالَ لَهُ «صُمْ يَوْمًا وَلَكَ أَجْرُ مَا بَقِيَ» قَالَ إِنِّي أُطِيقُ أَكْثَرَ مِنْ ذَلِكَ قَالَ «صُمْ يَوْمَيْنِ وَلَكَ أَجْرُ مَا بَقِيَ» قَالَ إِنِّي أُطِيقُ أَكْثَرَ مِنْ ذَلِكَ قَالَ «صُمْ ثَلَاثَةَ أَيَّامٍ وَلَكَ أَجْرُ مَا بَقِيَ» قَالَ إِنِّي أُطِيقُ أَكْثَرَ مِنْ ذَلِكَ قَالَ «صُمْ أَرْبَعَةَ أَيَّامٍ وَلَكَ أَجْرُ مَا بَقِيَ» قَالَ إِنِّي أُطِيقُ أَكْثَرَ مِنْ ذَلِكَ قَالَ «صُمْ أَفْضَلَ الصِّيَامِ عِنْدَ اللهِ صَوْمَ دَاوُدَ كَانَ يَصُومُ يَوْمًا وَيُفْطِرُ يَوْمًا»  

'Amr said: "I spoke to the Prophet and he said: 'Fast one day out of ten and you will have the reward of the other nine.' I said: 'I am able to do more than that.' He said: 'Fast one day out of eight and you will have the reward of the other eight.' I said: 'I am able to do more than that.' He said: 'Fast one day out of eight and you will have the reward of the other seven.' I said: 'I am able to do more than that.' 'Fast one day and not the next."' (Using translation from Nasāʾī 2395)  

«صُمْ مِنْ كُلِّ عَشَرَةِ أَيَّامٍ يَوْمًا وَلَكَ أَجْرُ تِلْكَ التِّسْعَةِ» فَقُلْتُ إِنِّي أَقْوَى مِنْ ذَلِكَ قَالَ «فَصُمْ مِنْ كُلِّ تِسْعَةِ أَيَّامٍ يَوْمًا وَلَكَ أَجْرُ تِلْكَ الثَّمَانِيَةِ» فَقُلْتُ إِنِّي أَقْوَى مَنْ ذَلِكَ قَالَ «فَصُمْ مِنْ كُلِّ ثَمَانِيَةِ أَيَّامٍ يَوْمًا وَلَكَ أَجْرُ تِلْكَ السَّبْعَةِ» قُلْتُ إِنِّي أَقْوَى مِنْ ذَلِكَ قَالَ فَلَمْ يَزَلْ حَتَّى قَالَ «صُمْ يَوْمًا وَأَفْطِرْ يَوْمًا»  

[Machine] The Messenger of Allah ﷺ said to him, "Fast for one day and you will have the reward of ten days." He said, "Increase me, O Messenger of Allah." He said, "Fast for two days and you will have the reward of nine days." He said, "Increase me." He said, "Fast for three days and you will have the reward of eight days." Thabit said, "So I informed Muattib ibn Abdullah about that, and he said, 'I do not see anything except that it increases in action and decreases in reward.'" Abu Abdullah added, "Some of them increased upon others."  

إِنَّ رَسُولَ اللهِ ﷺ قَالَ لَهُ «صُمْ يَوْمًا وَلَكَ أَجْرُ عَشَرَةِ أَيَّامٍ» قَالَ قُلْتُ زِدْنِي يَا رَسُولَ اللهِ قَالَ «صُمْ يَوْمَيْنِ وَلَكَ تِسْعَةٌ» قَالَ قُلْتُ زِدْنِي قَالَ «صُمْ ثَلَاثَةَ أَيَّامٍ وَلَكَ أَجْرُ ثَمَانِيَةِ أَيَّامٍ» قَالَ ثَابِتٌ فَأَخْبَرْتُ بِذَلِكَ مُطَرِّفَ بْنَ عَبْدِ اللهِ فَقَالَ مَا أُرَاهُ إِلَّا يَزْدَادُ فِي الْعَمَلِ وَيَنْقُصُ مِنَ الْأَجْرِ قَالَ أَبُو عَبْدِ الرَّحْمَنِ زَادَ بَعْضُهُمْ عَلَى بَعْضٍ