Sayyiduna Abdullah ibn Abbas (may Allah be pleased with them both) narrates: When the Prophet Muhammad (peace and blessings be upon him) arrived in Madinah, he saw that the Jews were fasting on the day of Ashura. The Prophet (peace be upon him) asked: "Why do you fast on this day?" They replied: "This is a great day in which Allah granted deliverance to Sayyiduna Musa (peace be upon him) and drowned the army of Pharaoh on this day. Sayyiduna Musa (peace be upon him) fasted on this day out of gratitude." The Prophet (peace be upon him) said: "We are closer to Sayyiduna Musa (peace be upon him) than you." So the Prophet (peace be upon him) fasted on this day and ordered fasting on this day.