It is narrated from Umm al-Mu'minin Hazrat Aisha (may Allah be pleased with her) that in the days of ignorance, the Quraysh used to fast on the tenth of Muharram, and the Prophet (peace and blessings of Allah be upon him) also used to fast on this day. After migrating to Madinah, the Prophet (peace and blessings of Allah be upon him) continued to fast on this day and instructed his companions (may Allah be pleased with them) to fast as well. Then, when the fasting of the month of Ramadan was made obligatory, the Prophet (peace and blessings of Allah be upon him) began to fast only in Ramadan and abandoned the fast of Ashura. Now, whoever wishes may fast, and whoever wishes may leave it.