It is narrated from Hazrat Humaid bin Abdur Rahman that Sayyiduna Muawiyah (may Allah be pleased with him) came to Madinah Munawwarah on the day of Ashura, and while delivering a sermon, he said: "O people of Madinah, where are your scholars? I heard the Messenger of Allah (peace and blessings be upon him) say: 'This is the day of Ashura. Fasting on this day has not been made obligatory upon you. However, I am fasting, so whoever wishes to fast may do so.'" Imam Abu Bakr (may Allah have mercy on him) says that "lam" (did not) is used only for the past.