When Allah's Messenger (ﷺ) arrived at Medina, he found the Jews observing the fast on the day of 'Ashura'
(10th of Muharram). The Prophet (ﷺ) asked them (about it) and they replied, "This is the day when Moses
became victorious over Pharaoh." The Prophet (ﷺ) said (to the Muslims), "We are nearer to Moses than
they, so fast on this day."
Sahih al-Bukhari Book 65, Hadith 259