عَنْ عَلِيٍّ رَضِيَ اللَّهُ عَنْهُ أَنَّ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَآلِهِ وَسَلَّمَ كَانَ يَصُومُ يَوْمَ عَاشُورَاءَ، وَيَأْمُرُ بِهِ
It is narrated from Sayyiduna Ali (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) himself used to fast on the Day of Ashura and also used to order (others) to fast on it.