'It was said to the Prophet that a man fasted for the rest of his life. He said: 'I wish that he had never eaten.' They said: 'Two-thirds (of a lifetime)?' He said: 'That is too much.' Then he said: 'Shall I not tell you of that which will take away impurity from the heart? Fasting 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."
Sunan an-Nasa'i Book 22, Hadith 296
← Previous Hadith "O Messenger of Allah, I am a man who fasts continually: shoud I fast when traveling?" He said: "Fast if you wish and break you fast if you wish." 'Ata said: "someone who heard him told me that Ibn 'Umar (said) that the Prophet said: 'Whoever fasts every day of his life, and then he has not fasted."

Sunan an-Nasa'i Book 22, Hadith 295 Next Hadith → "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."

Sunan an-Nasa'i Book 22, Hadith 297