Musannaf Ibn Abi Shaybah 9607 — Fasting the day of Ashura

Sayyidah Aishah (may Allah be pleased with her) said: Quraysh used to fast on the day of Ashura in the time of Jahiliyyah. When the Messenger of Allah (peace and blessings be upon him) came to Madinah, he fasted on Ashura and ordered the Muslims too to fast on that day. When the fasts of Ramadan were made obligatory, Ramadan became the obligation and the fast of Ashura was left. So whoever wished fasted it, and whoever wished left it.