Narrated Ibn `Abbas: When the Prophet (peace be upon him) arrived at Medina, the Jews were observing the fast on ‘Ashura’ (10th of Muharram) and they said, “This is the day when Moses became victorious over Pharaoh,” On that, the Prophet (peace be upon him) said to his companions, “You (Muslims) have more right to celebrate Moses’ victory than they have, so observe the fast on this day.”
Sahih al-Bukhari, Vol. 6, Book 65, Hadith 4680
