It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "Today is the day of Ashura, so whoever wishes may fast on this day, and whoever wishes may not fast." The narrations of Sayyidah Aisha and Muawiyah (may Allah be pleased with them both) are also related to this issue.