Narrated AbuQatadah:

A man came to the Prophet ﷺ and said: How do you fast, Messenger of Allah? The Messenger of Allah ﷺ became angry at what he said.

When Umar observed this (his anger), he said: We are satisfied with Allah as Lord, with Islam as religion, and with Muhammad as Prophet. We seek refuge in Allah from the anger of Allah, and from the anger of His Apostle. Umar continued to repeat these words till his anger cooled down. He then asked: Messenger of Allah, what is the position of one who observes a perpetual fast?

He replied: May he not fast or break his fast. Musaddad said in his version: He has neither fasted nor broken his fast. The narrator, Ghaylan, doubted the actual wordings.

He asked: What is the position of one who fasts two days and does not fast one day?

He said: Is anyone able to do that? He asked: What is the position of one who fasts every second day (i.e. fasts one day and does not fasts the next day)?

He (the Prophet) said: This is the fast that David observed.

He asked: Messenger of Allah, what is the position of one who fasts one day and breaks it for two days? He replied: I wish I were given the power to observe that. Then the Messenger of Allah ﷺ said: The observance of three days' fast every month and of one Ramadan to the other (i.e. the fast of Ramadan every year) is (equivalent to) a perpetual fast. I seek from Allah that fasting on the day of Arafah may atone for the sins of the preceding and the coming year, and I seek from Allah that fasting on the day of Ashura' may atone for the sins of the preceding year.

حَدَّثَنَا سُلَيْمَانُ بْنُ حَرْبٍ، وَمُسَدَّدٌ، قَالاَ حَدَّثَنَا حَمَّادُ بْنُ زَيْدٍ، عَنْ غَيْلاَنَ بْنِ جَرِيرٍ، عَنْ عَبْدِ اللَّهِ بْنِ مَعْبَدٍ الزِّمَّانِيِّ، عَنْ أَبِي قَتَادَةَ، أَنَّ رَجُلاً، أَتَى النَّبِيَّ ﷺ فَقَالَ يَا رَسُولَ اللَّهِ كَيْفَ تَصُومُ فَغَضِبَ رَسُولُ اللَّهِ ﷺ مِنْ قَوْلِهِ فَلَمَّا رَأَى ذَلِكَ عُمَرُ قَالَ رَضِينَا بِاللَّهِ رَبًّا وَبِالإِسْلاَمِ دِينًا وَبِمُحَمَّدٍ نَبِيًّا نَعُوذُ بِاللَّهِ مِنْ غَضَبِ اللَّهِ وَمِنْ غَضَبِ رَسُولِهِ . فَلَمْ يَزَلْ عُمَرُ يُرَدِّدُهَا حَتَّى سَكَنَ غَضَبُ رَسُولِ اللَّهِ ﷺ . فَقَالَ يَا رَسُولَ اللَّهِ كَيْفَ بِمَنْ يَصُومُ الدَّهْرَ كُلَّهُ قَالَ " لاَ صَامَ وَلاَ أَفْطَرَ " . قَالَ مُسَدَّدٌ " لَمْ يَصُمْ وَلَمْ يُفْطِرْ أَوْ مَا صَامَ وَلاَ أَفْطَرَ " . شَكَّ غَيْلاَنُ . قَالَ يَا رَسُولَ اللَّهِ كَيْفَ بِمَنْ يَصُومُ يَوْمَيْنِ وَيُفْطِرُ يَوْمًا قَالَ " أَوَيُطِيقُ ذَلِكَ أَحَدٌ " . قَالَ يَا رَسُولَ اللَّهِ فَكَيْفَ بِمَنْ يَصُومُ يَوْمًا وَيُفْطِرُ يَوْمًا قَالَ " ذَلِكَ صَوْمُ دَاوُدَ " . قَالَ يَا رَسُولَ اللَّهِ فَكَيْفَ بِمَنْ يَصُومُ يَوْمًا وَيُفْطِرُ يَوْمَيْنِ قَالَ " وَدِدْتُ أَنِّي طُوِّقْتُ ذَلِكَ " . ثُمَّ قَالَ رَسُولُ اللَّهِ ﷺ " ثَلاَثٌ مِنْ كُلِّ شَهْرٍ وَرَمَضَانُ إِلَى رَمَضَانَ فَهَذَا صِيَامُ الدَّهْرِ كُلِّهِ وَصِيَامُ عَرَفَةَ إِنِّي أَحْتَسِبُ عَلَى اللَّهِ أَنْ يُكَفِّرَ السَّنَةَ الَّتِي قَبْلَهُ وَالسَّنَةَ الَّتِي بَعْدَهُ وَصَوْمُ يَوْمِ عَاشُورَاءَ إِنِّي أَحْتَسِبُ عَلَى اللَّهِ أَنْ يُكَفِّرَ السَّنَةَ الَّتِي قَبْلَهُ " .