Sahih Bukhari
Sahih Bukhari Volume 003, Book 031, Hadith Number 223.
Hadith Section/Book: Sahih Bukhari Sahih Bukhari Book 31. Fasting
Narated By Abu Musa : The day of 'Ashura' was considered as 'Id day by the Jews. So the Prophet ordered, "I recommend you (Muslims) to fast on this day."