“Whoever fasts three days in every month, that is fasting for a lifetime.” Then, in testimony of that, Allah revealed: “Whoever brings a good deed shall have ten time the like thereof to his credit.” [6:160] So one day is equivalent to ten (in reward).
قَالَ رَسُولُ اللَّهِ ﷺ مَنْ صَامَ ثَلاَثَةَ أَيَّامٍ مِنْ كُلِّ شَهْرٍ فَذَلِكَ صَوْمُ الدَّهْرِ فَأَنْزَلَ اللَّهُ ﷻ تَصْدِيقَ ذَلِكَ فِي كِتَابِهِ {مَنْ جَاءَ بِالْحَسَنَةِ فَلَهُ عَشْرُ أَمْثَالِهَا} فَالْيَوْمُ بِعَشْرَةِ أَيَّامٍ
"The Messenger of Allah said: 'Whoever fasts for three days of each month, he has fasted for a whole lifetime.' Then he said: Allah has spoken the truth in His book: Whoever brings a good deed shall have ten times the like thereof to his credit.
قَالَ رَسُولُ اللَّهِ ﷺ مَنْ صَامَ ثَلاَثَةَ أَيَّامٍ مِنَ الشَّهْرِ فَقَدْ صَامَ الدَّهْرَ كُلَّهُ ثُمَّ قَالَ صَدَقَ اللَّهُ فِي كِتَابِهِ { مَنْ جَاءَ بِالْحَسَنَةِ فَلَهُ عَشْرُ أَمْثَالِهَا }
"The Messenger of Allah said: 'Whoever fasts three days in every month, then that is (similar to) fasting every day.' Then Allah Mighty and Sublime is He, attested to that in His Book, by revealing: Whoever brings a good deed, shall have ten times the like thereof. So a day is like ten."
قَالَ رَسُولُ اللَّهِ ﷺ مَنْ صَامَ مِنْ كُلِّ شَهْرٍ ثَلاَثَةَ أَيَّامٍ فَذَلِكَ صِيَامُ الدَّهْرِ فَأَنْزَلَ اللَّهُ ﷻ تَصْدِيقَ ذَلِكَ فِي كِتَابِهِ (مَنْ جَاءَ بِالْحَسَنَةِ فَلَهُ عَشْرُ أَمْثَالِهَا ) الْيَوْمُ بِعَشَرَةِ أَيَّامٍ
[Machine] The Messenger of Allah ﷺ said, "Whoever fasts three days of the month, let him fast the entire month." Then he said, "Allah and His Messenger spoke the truth in His Book, 'Whoever comes with a good deed will have ten times its like.'" [Al-Anam: 160]
قَالَ رَسُولُ اللهِ ﷺ «مَنْ صَامَ ثَلَاثَةَ أَيَّامٍ مِنَ الشَّهْرِ فَلْيَصُمِ الدَّهْرَ كُلَّهُ» ثُمَّ قَالَ صَدَقَ اللهُ وَرَسُولُهُ فِي كِتَابِهِ {مَنْ جَاءَ بِالْحَسَنَةِ فَلَهُ عَشْرُ أَمْثَالِهَا} [الأنعام 160]
" عَنْ عَلىٍّ عَنِ النبِيّ ﷺ قَالَ: صِيامُ ثَلاَثَةِ أَيَّامٍ مِنْ كلِّ شهْرٍ صيَامُ الدَّهْرِ، كلُّ يَوْمٍ عَشْرَةُ أَيَّامٍ، مَنْ جاءَ بِالْحَسَنَةِ فَلَهُ عَشْرُ أَمْثالِها ".
"عَنْ أَبِى ذَرٍّ قَالَ: قَالَ رَسُولُ الله ﷺ صِيَامُ ثَلَاثَةِ أَيَّامٍ مِنْ كُلِّ شَهْرٍ كصِيَامِ السنَةِ كُلِّهَا، قَالَ: فَصَدَّقَ الله ورَسُولَه ﷺ في كِتَابِهِ، فَقَالَ: {مَن جَاءَ بِالْحَسَنَةِ فَلَهُ عَشْرُ أَمْثَالِهَا} ".