“The Day of ʿĀshūrāʾ was a day that Quraysh used to fast during the pre-Islamic period of ignorance, and the Prophet — may Allah’s peace and blessings be upon him — used to fast it as well. When he came to Madīnah, he fasted it and commanded its observance. Then, when the fasting of Ramaḍān was prescribed, Ramaḍān became the obligatory fast, and ʿĀshūrāʾ was abandoned. Thus, whoever wished to fast it did so, and whoever wished not to fast it left it.”

Narrated by al-Bukhārī (no. 4504) — his wording — and by Muslim (no. 1125), from the narration of ʿĀʾishah (may Allah be pleased with her).
Also narrated by Muslim (no. 1126), from the narration of ʿAbd Allāh ibn ʿUmar (may Allah be pleased with them both): “And the Messenger of Allah — may Allah’s peace and blessings be upon him — used to fast it, and so did the Muslims, before the fasting of Ramaḍān was made obligatory.”

Brief Explanation of the Hadith

Among the virtuous days that the Sunnah has mentioned and clarified the merit of is the Day of ʿĀshūrāʾ — the tenth day of the sacred month of Allah, al-Muḥarram. It is a great day on which Allah saved Mūsā (peace be upon him) and his people, and drowned Pharaoh and his people. The Sunnah has also explained the stages of legislation concerning its fasting, as illustrated in the ḥadīth of the Mother of the Believers, ʿĀʾishah (may Allah be pleased with her). Quraysh used to fast on this day during the pre-Islamic period of ignorance (Jāhiliyyah), as did the Arabs before Islam — despite their ignorance of Allah and His laws, and their worship of idols. Yet they still revered this day and observed fasting upon it, which indicates that it held significance and esteem among them. It is likely that they inherited this practice from a previous divine law, for they used to honor this day by clothing the Kaʿbah and through other acts of veneration.
The Prophet — may Allah’s peace and blessings be upon him — used to fast on this day in Makkah before the Hijrah, in agreement with Quraysh in what they practiced of good deeds — and this was the first stage of fasting on the Day of ʿĀshūrāʾ.
In the second year after the Hijrah, he found that the Jews also fasted on this day, so he asked them about the reason for their fasting. They replied: “It is a righteous day — Allah saved Moses and drowned Pharaoh on it.” He said, “We have more right to Moses than you,” so he fasted on that day and commanded that it be fasted. This was the second stage of its legislation, during which fasting on ʿĀshūrāʾ appeared to be obligatory. A group of scholars held that fasting on the Day of ʿĀshūrāʾ was indeed obligatory in the beginning, based on the apparent meaning, but its obligation was abrogated when the fast of Ramadān was prescribed — for no other fast is obligatory besides it. Thus, fasting on ʿĀshūrāʾ became a recommended act, not an obligation; whoever wishes may fast it, and whoever wishes may leave it. Others said that fasting on that day was never obligatory at all, and they interpreted the Prophet’s command as an emphatic recommendation and a sign of great concern for it. This represents the third stage of its legislation. The scholars unanimously agreed on the recommendation of fasting the Day of ʿĀshūrāʾ.
As for her saying, may Allah be pleased with her, “When he came to Madīnah, he fasted it,” it is not meant in the immediate temporal sense. Rather, the meaning is that after his arrival and settlement there—in the second year after the Hijrah—when the Day of ʿĀshūrāʾ came, he fasted it and commanded its observance.
The ḥadīth also indicates the virtue of the Day of ʿĀshūrāʾ and its veneration both in the pre-Islamic period and in Islam.
It also indicates that fasting it was initially obligatory, then its ruling was abrogated to that of recommendation, according to a group of scholars. It further demonstrates the permissibility of abrogation (naskh) within Islamic law. Moreover, it shows that the Prophet — may Allah’s peace and blessings be upon him — would concur with Quraysh in the virtuous acts they practiced, such as fasting on the Day of ʿĀshūrāʾ, performing ḥajj, and ʿumrah.