"A man came to the Messenger of Allah and said: 'O Messenger of Allah, what do you say about a man who fated for the rest of his life?' The Messenger of Allah said: 'I wish that he would never eat for the rest of his life.' He said: 'Two-thirds ( of a lifetime)?' he said: 'That is too much.' He said: 'Half?' He said: 'Shall I not tell you of that which will take away impurity from the heart?' He said: 'Yes.' He said: 'Fasting for three days each month."' 'Ata said: "someone who heard him told me that Ibn 'Umar (said) that the Prophet said: 'Whoever fasts every day of his life, then he has not fasted." (Using translation from Nasāʾī 2386)
أَتَى رَسُولَ اللهِ ﷺ رَجُلٌ فَقَالَ يَا رَسُولَ اللهِ مَا تَقُولُ فِي رَجُلٍ صَامَ الدَّهْرَ؟ فَقَالَ رَسُولُ اللهِ ﷺ «وَدِدْتُ أَنَّهُ لَمْ يَطْعَمِ الدَّهْرَ شَيْئًا» قَالَ فَثُلُثَيْهِ؟ قَالَ «أَكْثَرَ» قَالَ فَنِصْفَهُ قَالَ «أَكْثَرَ أَلَا أُخْبِرُكُمْ بِمَا يُذْهِبُ وَحَرَ الصَّدْرِ؟» قَالُوا بَلَى قَالَ «صَوْمُ ثَلَاثَةِ أَيَّامٍ مِنْ كُلِّ شَهْرٍ»