Musnad Ahmad

It is narrated from Hazrat Abu Qatadah Ansari (may Allah be pleased with him) that a man asked the Holy Prophet (peace and blessings be upon him), "O Messenger of Allah (peace and blessings be upon him)! If a person fasts all the time, what is the ruling?" The Holy Prophet (peace and blessings be upon him) said, "His fasting and not fasting are both the same." The questioner asked, "How about fasting for two days and leaving one day?" The Holy Prophet (peace and blessings be upon him) said, "Who has the strength for that?" The questioner asked, "How about leaving two days and fasting one day?" The Holy Prophet (peace and blessings be upon him) said, "Perhaps this is praiseworthy in the sight of Allah." The questioner asked, "How about fasting one day and leaving one day?" The Holy Prophet (peace and blessings be upon him) said, "That is the way of my brother, Hazrat Dawood (peace be upon him)." The questioner asked about fasting on Mondays and Thursdays. The Holy Prophet (peace and blessings be upon him) said, "On that day I was born and on that day revelation was sent down to me. Fasting three days in every month and fasting the whole month of Ramadan is equal to fasting all the time." The questioner asked, "What is the ruling on fasting on the Day of Arafah?" The Holy Prophet (peace and blessings be upon him) said, "It is an expiation for the sins of the previous and coming year." The questioner asked about the ruling of fasting on the Day of Ashura, so he said, "It is an expiation for the sins of the previous year."