Muwatta Imam Malik Book of Fasting, Hadith 34

Yahya related to me from Malik from Ibn Shihab that Humayd ibn Abd ar-Rahman ibn Awf heard Muawiya ibn Abi Sufyan say from the mimbar on the day of Ashura in the year in which he made the hajj, "People of Madina, where are your learned men? I heard the Messenger of Allah ﷺ say about this day, 'This is the day of Ashura, and fasting it has not been prescribed for you. I am fasting it, and whoever of you wants to fast it can do so, and whoever does not want to, does not have to.' "

وَحَدَّثَنِي عَنْ مَالِكٍ، عَنِ ابْنِ شِهَابٍ، عَنْ حُمَيْدِ بْنِ عَبْدِ الرَّحْمَنِ بْنِ عَوْفٍ، أَنَّهُ سَمِعَ مُعَاوِيَةَ بْنَ أَبِي سُفْيَانَ، يَوْمَ عَاشُورَاءَ عَامَ حَجَّ وَهُوَ عَلَى الْمِنْبَرِ يَقُولُ يَا أَهْلَ الْمَدِينَةِ أَيْنَ عُلَمَاؤُكُمْ سَمِعْتُ رَسُولَ اللَّهِ ﷺ يَقُولُ لِهَذَا الْيَوْمِ " هَذَا يَوْمُ عَاشُورَاءَ وَلَمْ يُكْتَبْ عَلَيْكُمْ صِيَامُهُ وَأَنَا صَائِمٌ فَمَنْ شَاءَ فَلْيَصُمْ وَمَنْ شَاءَ فَلْيُفْطِرْ " .