Sunan an-Nasa'i 2433

It was narrated from Abu Nawfal bin Abi 'Aqrab that his father said:"I asked the Messenger of Allah about fasting and he said: 'Fast one day of the month.' I said: 'Fast one day of the month.' I said: 'O Messenger of Allah, let me do more, let me do more.' He said: 'Let me do more, let mo do more; I am able for it.' Then the Messenger of Allah fell silent until I thought that he was going to refuse my request. Then he said: 'fast three days of each month