Wednesday night and Thursday is the most tragic day in the Jewish calendar, Tisha B’Av. it commemorates a number of terrible events that occurred on that day, including the destruction of both Temples in Jerusalem. It is a fast day for Jews.
This year, however, tens of millions – maybe hundreds of millions - of Muslims will be fasting on that same day.
The ninth day of Dhu'l-Hijjah (the 12th and final month of the Islamic calendar) is the Day of 'Arafah. It is the day when pilgrims stand on the plain of 'Arafah to pray. On this day, Muslims all over the world who do not witness the annual Hajj should spend the day in fasting.
The Day of Arafah is more like Yom Kippur than Tisha B’Av – according to Muslim legend, those that fast on that day will be forgiven not only for the previous year’s sins but for the coming year’s sins as well. This brings up interesting theological questions.
However, fasting on that day is a custom, not obligatory, for Muslims.
Since very few Muslims are going on pilgrimage to Mecca this year, and the Muslim population was smaller that last time Tisha B’Av coincided with the Day of Arafah, that means that this year there will be more people fasting on Tisha B’Av than at any time in history. Of course, the vast majority aren’t Jewish.
(h/t Yerushalimey)