It was narrated that Ibn ‘Abbas (رضي الله عنه) said:

When the Messenger of Allah (ﷺ) came to Madinah, he saw the Jews fasting on the day of 'Ashoora'. He asked they about that and they said: This is the day on which Moosa prevailed over Pharaoh. The Prophet (ﷺ) said to his Companions: "You are closer to Moosa than them, so fast (on this day)."