Sayyiduna Ibn Abbas (may Allah be pleased with them both) narrates that when the Noble Prophet (peace and blessings be upon him) arrived in Madinah Munawwarah, he found the Jews observing the fast of Ashura. When they were asked about this, they replied that on this day Allah Almighty granted Musa (peace be upon him) and the Children of Israel victory and dominance over Pharaoh, so they fast on this day to honor it. The Messenger of Allah (peace and blessings be upon him) said: "We are closer and more deserving of Musa (peace be upon him) than you." And he (peace and blessings be upon him) ordered the observance of fasting on this day. A narration from Abu Bishr is also reported in the same manner. In it, it is mentioned that "He (the Prophet) fasted on the day of Ashura and also ordered fasting on this day." Imam Abu Bakr (may Allah have mercy on him) says that Imam Muslim bin Hajjaj had asked me about this matter.