Yahya related to me from Malik that he used to hear the people ofknowledge say,"There is no harm in fasting continuously as long as onebreaks the fast on the days on which the Messenger of Allah, may Allahbless him and grant him peace, forbade fasting, namely, the days ofMina, the day of Adha and the day of Fitr, according to what we haveheard."Malik said, "This is what I like most out of what Ihave heard about the matter."
USC-MSA web (English) reference: Book 18, Hadith 37
Arabic reference: Book 18, Hadith 671