Sayyidah Ayshah (RA) said that the Quraysh used to fast on the day of Ashura in the Days of Jahiliyah. And Allah’s Messenger (SAW) also used to fast. When he came to Madinah, he used to fast and he commanded the people to fast. But when the fasts of Ramadan were prescribed, they became lard and the Ashura was given up. So he who wished fasted (on that day) and he who wished did not (fast).
[Ahmed26127, Bukhari 4502, Muslim 1125, Ibn e Majah 1733, Abu Dawud 2442]