Sahih al-Bukhari 2004

Abū Maʿmar related to us: ʿAbd al-Wārith related to us: Ayyūb related to us: ʿAbd Allāh ibn Saʿīd ibn Jubayr related to us, from his father, from Ibn ʿAbbās (may Allah be pleased with them both), who said: The Prophet (Allah bless him and grant him peace) came to Madinah and saw the Jews fasting on the Day of ʿĀshūrāʾ. He asked, ‘What is this?’ They replied, ‘This is a good day; it is the day on which Allah saved the Children of Israel from their enemy, and Moses fasted on it.’ He said, ‘We have a greater claim to Moses than you.’ So he fasted that day and commanded that it be fasted.