Yaum-e-Ashura (the tenth day of Muharram)

What is Ashura and what is it's significance in Islam?

As per Islamic calendar, today (Ashura) is the day when...

the world was made;
when Adam (AS) was created (years later);
when Abraham (Ibrahim) (AS) was saved from Nimrod's fire;
when Noah's (Nuh) (AS) ark was delivered from the floods;
when Joseph (Yusuf) (AS) was reunited with his father Jacob (Yakub) (AS);
Jonah (Yunus) (AS) was saved from the fish's (probably whale) belly;
Job (Ayyub) (AS) was cured of leprosy;
the kingdom of Solomon (Sulaiman) (AS) was restored;
David (Dawood) (AS) was forgiven;
Jesus (Isaa) (AS) was born;
Jesus was taken up to the heavens by replacing him with a lookalike who was crucified;

And not to forget, the martyrdom of Imaam Hussain (grandson of Mohammed SAS) in the battle of karbala by the evil King Yazeed who proclaimed to be God-like). This battle was fought so that Islam would not be diluted by wrong practices, which Yazeed wished to introduce after proclaiming himself as Islamic leader. It could have also led to editing of Quran by individuals. Though Hussain was killed when prostrating in prayer (offering namaaz) in battle; his martyrdom was in fact a victory. Cause after that there was awareness against Yazeed and clarity in the religion.

From the events over the ages, it is evident that God loves the day of Ashura (10th day of Muharram) and He even forgave many Prophets and gave mercy to those He was testing on this day (this is God's way of saying that everyone is capable of error and tests, including Prophets). So keep praying and keep seeking forgiveness on this day.

And yeah, like my Dad always says Never Work on Ashura. Since has been the norm since ages, even before the advent of Islam.

The Arabic word Ashura means 'tenth' and is derived from Hebrew word Asarah or Asharah.

What we call Yaum-e-Ashura (Yaum meaning Day, together meaning 'tenth day') is similar to Yom-e-Kippur (Day of Atonement) in Judaism. This is the tenth day of Jewish month of Tishri. So for many years before Islam also, this day had a lot of significance due to it's glorious history. 

Muhammad SAS used to fast on the day of Ashura, (10th of Muharram), in Makkah. When Muhammad SAS led his followers to Madina, he found that the Jews of that area likewise observed fasts on the day of Ashura. At this, Muhammad affirmed the Islamic claim to the fast, and from then on the Muslims have fasted on combinations of two consecutive days including the 10th of Muharram (e.g. 9th and 10th or 10th and 11th) to differentiate between the practices of the two faiths. Due to minor differences in a day or two in months due to moon, these days might not been occurring on same dates now is my understanding. 

So while the fasts of Ramzan are compulsory, the fasting of two days around Ashura are 'recommended' and to be done in combination of two.