Sayyiduna Salamah bin Akwa’ (may Allah be pleased with him) narrates: The Prophet Muhammad (peace and blessings be upon him) sent a man from the tribe of Aslam to announce among the people: “Today is the day of Ashura. Whoever has eaten something should not eat anything for the rest of the day, and whoever has not eaten or drunk anything should observe the fast.”
Hadith Referenceصحیح ابن حبان / كتاب الصوم / 3619
Hadith Gradingفضيلة الشيخ الإمام محمد ناصر الدين الألبانيصحيح - المصدر نفسه: ق.فضيلة الشيخ العلّامة شُعيب الأرناؤوطإسناده صحيح على شرط الشيخين