Sahih Bukhari
Sahih Bukhari Volume 003, Book 031, Hadith Number 224.
Hadith Section/Book: Sahih Bukhari Sahih Bukhari Book 31. Fasting
Narated By Ibn 'Abbas : I never saw the Prophet seeking to fast on a day more (preferable to him) than this day, the day of 'Ashura', or this month, i.e. the month of Ramadan.