Nasai

´It was narrated from 'Amr bin Shurahbil that a man from among the Companions of the Prophet said:` '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."

´It was narrated that 'Amr bin Shurahbil said:` "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."

´It was narrated that Abu Qatadah said:` "Umar said: 'O Messenger of Allah, what about a person who fasted for an entire lifetime?' He said: 'He neither fasted nor broke his fast for one day?' He said: 'Can anyone do that?' He said: 'What about a person who fasted for one day?' He said: 'That is the fast of Dawud, peace be upon him.' He said: 'What about a person who fasted for one day, and broke his fast for two days?' he said: 'I wish that I could do that.' Then he said: 'Three days of each month, and from Ramadan to Ramadan, this is fasting for an entire lifetime."' '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."