The day of 'Ashura was one which the Jews respected and they treated it as Id. The Messenger of Allah ﷺ said: You also observe fast on this day.
كَانَ يَوْمُ عَاشُورَاءَ يَوْمًا تُعَظِّمُهُ الْيَهُودُ وَتَتَّخِذُهُ عِيدًا فَقَالَ رَسُولُ اللَّهِ ﷺ صُومُوهُ أَنْتُمْ