Imam Ahmad narrated
in the Musnad (his book of Hadith) through the route of Abu Hurayrah that once the Prophet passed by a group of Jews in Madinah. The Prophet realized that they were fasting the " 10th day of Muharram ". The Prophet asked, “ Why are you fasting this day? ” They said this was the day when God rescued Prophet Moses and the Children of Israel from Pharaoh who drowned as well on that day. It was also the day the ark of Prophet Noah landed on Mount al-Judiyy. Noah and Moses fasted that day as an indication of their thankfulness to God. Then the Prophet said, “I am the one to fast that day ” and told his followers to fast the 10th of Muharram as well. He justified the reason for fasting that day by saying, “ We associate with Moses more than others do ”. The Prophet said this because Moses was Muslim as all the prophets, and we are more deserving of rejoicing his victory.