In the name of Almighty God, the Most Gracious, the Most Merciful. This past Sunday was the tenth day of the month of Muharram, which is for us Muslims, the holy day of Ashurah. The word "Ashurah" actually just means "ten" as it is the tenth day of the month, but the day had special significance for people who lived alongside the prophet Muhammad, peace and blessings be upon him.
When the prophet and his people made the Hijra, or the migration from Mecca to Yathrib (soon to be known as Medina), they found that the Jewish community in Yathrib commemorated the Exodus on this day. The Exodus for those who don't know was the freeing of Moses (peace be upon him) and the people of Israel from the bondage of Pharoah. The prophet Muhammad in seeing this said somewhat jokingly to the Jewish community "we have more right to Moses than you" (Bukhari, 1865). So, the prophet ordered the Muslims to also observe fasting on this day to remember the Exodus event. Later on when fasting during the month of Ramadan became obligatory on Muslims, fasting on Ashurah became optional.
Fasting on this day is an important source of blessing from Allah, as well as an important way of remembering one His greatest prophets, Moses (peace and blessings be upon him). It is also a day to remember our connection to our Jewish "cousins" in faith. In terms of law and lifestyle we have much more in common with the Jewish community than we do with the Christian community. Yet despite that there is so much animosity between us. People may think that this is an ancient rivalry and it's true there have been a few incidents throughout history. During the time of the prophet Muhammad (peace be upon him) there were some Jews who betrayed their agreement with the Prophet and thus were excommunicated and some cases executed as traitors by the Muslims. This was due to the fact that they had made bay'ah or a pledge to Muhammed to obey the laws of the Constitution of Medina (which you can find readily available online). This constitution gave the Jews of Medina equal rights under the law as it did to Muslims and to all who make a pledge to it and agree to help and protect other tribes who also made the pledge to it. Some of these Jews became traitors by assisting and allying with the Quraysh who were at war with the Muslims and other people of Medina.
Despite this, Jews and Muslims have historically got along. In Jerusalem, before Muslim rule there (under Christian rule) Jews were actually exiled from the city and banned from worshipping at the Wailing Wall (remnant of the old temple of Solomon peace be upon him). When Omar ibn Khattab, companion of the prophet Muhammad, rode into Jerusalem as it's new ruler, he respected Christian and Jewish places of worship and re-allowed Jews to live and worship in the city. Generally speaking Jews and Muslims were "on the same side" throughout most of history from that point on, both of which being constant targets of Christian persecution. Muslim, Jewish and Christian scientists and scholars studied and researched alongside each other in Baghdad and Cordoba, and in some cases houses of worship were used for all three religious traditions. It has only been in recent history, as in the past 60 years or so, that there has been significant tension between Muslim and Jewish people due to the founding and expansion of the state of Israel and the subsequent persecution of Palestinians.
Also the day of Ashurah has significance for Shia Muslims in that it is a day when they remember the death of Imam Hussein. Hussein was the grandson of the Prophet Muhammad (peace and blessings be upon him) and is revered by all Muslims as a great leader of the Muslims and revered by the Shia as one of their twelve Imams. Because of this, Ashurah is a more visibly celebrated holiday for the Shia, and the news media typically covers the Shia traditions that revolve around this day. However, it is indeed a day celebrated and commemorated by all Muslims and I sincerely hope all my brothers and sisters had a good Ashurah!
...And Allah Knows Best...