This is the day of Ashura, so fast on it, for the Messenger of Allah ﷺ said, "Fast on this day."
قال حدثنا الأسود بن عامر قال حدثنا إسرائيل قال حدثنا ثوير قال سمعت
هذا يوم عاشوراء فصوموا فإن رسول الله ﷺ قال صوموه
Its isnad is daif because of Thuwayr bin Abu Fakhita al-Kufi, they criticized his memory and accused him of being a Rafidi.