“The Messenger of Allah ﷺ used to fast ‘Ashura’, and he ordered (others) to fast it too.”  

كَانَ رَسُولُ اللَّهِ ﷺ يَصُومُ عَاشُورَاءَ وَيَأْمُرُ بِصِيَامِهِ  

If I live till the next (year), I would definitely observe fast on the 9th, and the narration transmitted by Abu Bakr is:" He meant the day of Ashura."  

قَالَ رَسُولُ اللَّهِ ﷺ لَئِنْ بَقِيتُ إِلَى قَابِلٍ لأَصُومَنَّ التَّاسِعَ وَفِي رِوَايَةِ أَبِي بَكْرٍ قَالَ يَعْنِي يَوْمَ عَاشُورَاءَ