Many reports suggest that during the early period of the Prophet's mission in Makkah, Muslims fasted on Muharram 10th; they started fasting for two days in Medina on the 10th and 9th or 11th of the month.
Ashura refers to the 10th of Muharram, and according to Muslim beliefs, this day was of great significance in all religious traditions.
However, on fasting on the 10th of Muharram, there are differences between Shia and Sunni scholars.
Shia Opinions
The renowned Shia researcher Muhaqqiq Qummi says that the fast of the day of 'Ashura came before the fast of Ramadan.
Sayyid 'Amili writes, "There are a lot of differing opinions about fasting on the day of 'Ashura. For example, was it wajib, or was it not? Our hadith recorded that fasting on the day of 'Ashura was wajib before the enactment of fasting in the holy month of Ramadan. Among the people narrated these hadiths are Zurarah and Muhammad ibn Muslim."
Allamah Majlisi relates from the book "Al-Muntaqi" that in the first year of migration to Medina, Allah's Prophet (S) fasted on 'Ashura, and the other people followed suit."
Upon study of the sayings of the Shi'ah scholars, one can infer that they have not put forward a definite opinion about fasting on the day of 'Ashura. Instead, they have contented themselves with narrating the differences among the scholars and in hadith. Only the renowned researcher Muhaqqiq Qummi has cited hadith that indicate the necessity of fasting on this day.
Sunni Opinions
Qadi 'Ayni says, "They have differed about the judgment of fasting during the early days of Islam. For example, Abu Hanifah believed it was wajib to fast on the day of 'Ashura in the past. But on the other hand, Shafi'i's companions have given two opinions: the most famous opinion is that it was highly recommended [mustahabb-e mu'akkad] right from the beginning of Islam and Islamic law, and never has it been wajib for the Islamic Ummah.
After the revelation of the Qur'anic verse enacting the fast of Ramadan, it remained mustahabb, but but lost the recommendation and emphasis it enjoyed before. The second opinion of Shafi'i's companions is similar to that of Abu Hanifah.
'Ayad has said that some predecessors used to believe this fast was wajib and remained wajib without any abrogation even after the verse enacting the fast of Ramadan. But supporters of this opinion have defeated, and hence common consensus is that this fast is not wajib, and they maintain that it is mustahabb."
Ibn Qudamah says, "There are differing opinions about the fast of the day of 'Ashura whether it was wajib or not. Qadi says it was wajib, which resulted from religious deduction and conclusion. He has deduced this using two rationales. It has also been quoted from Ahmad ibn Hanbal that the fast of the day of 'Ashura was wajib."
Kasani writes, "The fast of the day of 'Ashura was wajib during those days." 'Asqalani says that this fast was wajib."
However, Muslims, in general, remember Ashura as the day of the martyrdom of Imam Hussein. Imam Ibn Taymiya wrote the following about this greatest tragedy in early Islam.
و
أما من قتل الحسين أو أعان على قتله أو رضي بذلك فعليه لعنة الله والملائكة والناس أجمعين, ابن تيمية في مجموع الفتاوى 4 / 487
"The curse of God, the angels, and the entire community is on those who killed al-Hussein, assisted in killing him, or accepted his killing.
Ibn Taymiya, Majmou' al-Fatawa 4 / 487 فإن قتل الحسين وقتل عثمان من قبله كان من أعظم أسباب الفتن في هذه الامة وقتلتهما من شرار الخلق عند الله, ابن تيمية411 /3 الفتاوى
The killing of Hussein and Uthman before him is one of the great reasons for the temptations in the Muslim community, and God regards their killers as the worst of people / Majmou' al-Fatawa, Ibn Taymiya.
In our recent memory, the 10th of Muharram was the day when Imam Hussein, son of Ali, the cousin and son-in-law of Prophet Muhammad, offered his life together with his family members in the fields of Kerbala in Iraq. On this day, an army claiming to be Muslims confronted the grandson of the Prophet and denied him even water before decimating him and his family. It is a tragic day for Muslims, nay for all the people in the world, and the 10th of Muharram reminds us of that constantly.
Shias observe this day as a day of great mourning, reminding them of the sacrifices of Imam Hussein and his family. But on the other hand, Sunnis fast and usually avoid participating in events organized to commemorate the martyrdom of Imam Hussein.
Imam Hussein belongs to the entire Ummah, and his sacrifices are for the whole of the Ummah and not just for one section of the community. He stood for the principles of Islam and not just in the interests of one sect of the community. Imam fought for those eternal values of Islam that every Prophet preached to his people. He knew that life is sacred and a gift from Allah, yet he believed that there come times in the life of individuals when life's goals may become more important than life itself.
The goals of life he stood for are apparent. He believed people should not coerce people to elicit political allegiance to disagreed leaders. People have a right to dissent with rulers and leaders with dignity and honor. The resources of a nation belong to all and not to one dynasty, aristocracy, or elite group. Coercion and violence were weapons of despots in their campaign against truth and justice.
Thus, Imam Hussein challenged the decision of Ameer Muawiya, the ruler of the Muslim world at the time, one of the companions of the Prophet, when he nominated his son Yezid as his successor and turned Islamic polity into a monarchy.
Imam Hussein argues that Islam was against the dynastic rule, and the one selected by Ameer Muawiya was not qualified to lead the nation of Muslims. He was not alone in this opinion. Many of the companions in Medina and Makkah supported his ideas.
Against all odds, Imam Hussein challenged the forces of Yezid in Kerbala, realizing that those who had promised to be on his side had betrayed him. He knew that the oppressive forces would crush his family, and he would achieve martyrdom on the battlefield. Yet, the Imam decided to offer his life, primarily to prove the point that the goals of life are more important than life itself. He knew that compromise was not an option in these situations. However, he also realized that when the choice is so evident between right and wrong, one should offer all one has in defense of one's ideals. His ijtihad and actions emerged from his understanding of the Quran and the teachings of the Prophet.
It is this message Imam Hussein upheld and offered his martyrdom for. Unfortunately, one section of the community forgot it, and the other sect has highly expanded it. Shias mourn on this day. Suppose they mourn the loss of the grandson as a token of love. In that case, these occasions should be within limits because the mourning and repentance should belong to those who betrayed Imam Hussein and refused to support him even after inviting him to continue his resistance. By and large, Sunnis have remained silent on his martyrdom in general, not realizing that he stood for the principles his grandfather taught humanity.
The tenth of Muharram, thus, is a day of great significance in Muslim history as it is a day when one of the great leaders of the community, Imam Hussein, knowingly and consciously accepted martyrdom for saving the soul of Islam. It could be a day to bring Shias and Sunnis together because it was a day of pride when the grandson of the Prophet upheld the superiority of divine guidance over one's life and family. It was a day of deliverance.
Sunnis and Shias can focus on the message of the Imam and work to rid their world of despotism that has negated the essence of divine guidance.