Sunni Muslims look at Ashura as “good”
for different reasons:
The Prophet (peace and blessings of Allah be upon him) came to Madinah and saw the Jews fasting on the day of Ashoora. He said, “What is this?” They said, “This is a good day, this is the day when Allah saved the Children of Israel from their enemy and Moosa fasted on this day.” He (peace and blessings of Allah be upon him) said, “We are closer to Moosa than you.”
So the Prophet (peace and blessings of Allah be upon him) fasted on this day and told the people to fast.
There are many other versions of this Hadith in the books of “Muslim” and “Bukhari”.
According to a version narrated by Muslim,
This is a great day when Allah saved Moosa (Moses) and his people and drowned Pharaoh and his people.”
Muslims celebrate Ashura by fasting on that day. Usually, Muslims are recommended to fast either on the 9th and 10th of Muharram or on the 10th and 11th of Muharram.
It is permissible to fast the day of Ashoora on its own, but it is better to fast the day before it or the day after it. This is the Sunnah that is proven from the Prophet (peace and blessings of Allah be upon him), as he said, “If I am still alive next year, I will certainly fast the ninth.” Narrated by Muslim, 1134.
Other Ahadith on the subject are the following:
The prophet observed the fast on Ashuraa (the 10th of Muharram),
and ordered (Muslims) to fast on that day. (Agreed upon Hadith i.e. Bukhari & Muslim).
Narrated by Abi Katada: The prophet was asked about fasting on ‘Ashuraa’ (the 10th of Muharram), he said: "it expiates the previous year (for sins).” (Sahih Muslim)
While Shia believe that this day to be a day of mourning and sorrow and celebrate Ashura as you watch in the following pictures: