Umm al-Mu'mineen Sayyidah Aisha (may Allah be pleased with her) narrates: The day of Ashura was a day in which fasting was observed during the time of ignorance; this was before the command of Ramadan was revealed. When the command of Ramadan was revealed, then whoever wished could fast on this day, and whoever wished could leave fasting on this day.
Hadith Referenceمسند الحميدي / 202
Hadith Gradingمحدثین:إسناده صحيح
Hadith Takhrij«إسناده صحيح ، والحديث متفق عليه، وأخرجه البخاري: 1592، 1893، 2001، 2002، ومسلم: 1125، وابن حبان فى ” صحيحه“ : 3621، وأبو يعلى الموصلي فى ”مسنده“:4638»