Messenger of Allah ﷺ ordered (the Muslims) to fast on the day of 'Ashura', and when fasting in the month of Ramadan was prescribed, it became optional for one to fast on that day ('Ashura') or not.
كَانَ رَسُولُ اللَّهِ ﷺ أَمَرَ بِصِيَامِ يَوْمِ عَاشُورَاءَ فَلَمَّا فُرِضَ رَمَضَانُ كَانَ مَنْ شَاءَ صَامَ وَمَنْ شَاءَ أَفْطَرَ
(The tribe of) Quraish used to fast on the day of Ashura' in the Pre-Islamic period, and then Allah's Apostle ordered (Muslims) to fast on it till the fasting in the month of Ramadan was prescribed; whereupon the Prophet ﷺ said, "He who wants to fast (on 'Ashura') may fast, and he who does not want to fast may not fast."
أَنَّ قُرَيْشًا كَانَتْ تَصُومُ يَوْمَ عَاشُورَاءَ فِي الْجَاهِلِيَّةِ ثُمَّ أَمَرَ رَسُولُ اللَّهِ ﷺ بِصِيَامِهِ حَتَّى فُرِضَ رَمَضَانُ وَقَالَ رَسُولُ اللَّهِ ﷺ: «مَنْ شَاءَ فَلْيَصُمْهُ وَمَنْ شَاءَ أَفْطَرَ۔»
'A'isha (Allah be pleased with her) reported that the Messenger of Allah ﷺ had ordered to observe fast (on 'Ashura) before the fasting in Ramadan was made obligatory. But when it became obligatory, then he who wished fasted on the day of Ashura, and he who wished did not observe it (on that day).
كَانَ رَسُولُ اللَّهِ ﷺ يَأْمُرُ بِصِيَامِهِ قَبْلَ أَنْ يُفْرَضَ رَمَضَانُ فَلَمَّا فُرِضَ رَمَضَانُ كَانَ مَنْ شَاءَ صَامَ يَوْمَ عَاشُورَاءَ وَمَنْ شَاءَ أَفْطَرَ
[Machine] That the Prophet ﷺ used to recommend fasting on the day of Ashura before the month of Ramadan was made obligatory. So when Ramadan was made obligatory, whoever wished fasted and whoever wished broke their fast.
أَنَّ النَّبِيَّ ﷺ كَانَ يَأْمُرُ بِصِيَامِ عَاشُورَاءَ قَبْلَ أَنْ يَنْزِلَ رَمَضَانُ فَلَمَّا فُرِضَ رَمَضَانُ كَانَ مَنْ شَاءَ صَامَ وَمَنْ شَاءَ أَفْطَرَ
(The tribe of) Quraish used to fast on the day of Ashura' in the Pre-Islamic period, and then Allah's Apostle ordered (Muslims) to fast on it till the fasting in the month of Ramadan was prescribed; whereupon the Prophet ﷺ said, "He who wants to fast (on 'Ashura') may fast, and he who does not want to fast may not fast." (Using translation from Bukhārī 1893)
أَنَّ قُرَيْشًا كَانَتْ تَصُومُ يَوْمَ عَاشُورَاءَ فِي الْجَاهِلِيَّةِ ثُمَّ أَمَرَ رَسُولُ اللهِ ﷺ بِصِيَامِهِ حَتَّى فُرِضَ رَمَضَانُ فَقَالَ رَسُولُ اللهِ ﷺ «مَنْ شَاءَ فَلْيَصُمْهُ وَمَنْ شَاءَ أَفْطَرَهُ»
(The tribe of) Quraish used to fast on the day of Ashura' in the Pre-Islamic period, and then Allah's Apostle ordered (Muslims) to fast on it till the fasting in the month of Ramadan was prescribed; whereupon the Prophet ﷺ said, "He who wants to fast (on 'Ashura') may fast, and he who does not want to fast may not fast." (Using translation from Bukhārī 1893)
أَنَّ قُرَيْشًا كَانَتْ تَصُومُ عَاشُورَاءَ فِي الْجَاهِلِيَّةَ ثُمَّ أَمَرَ رَسُولُ اللهِ ﷺ بِصِيَامِهِ فَلَمَّا فُرِضَ رَمَضَانُ قَالَ رَسُولُ اللهِ ﷺ «مَنْ شَاءَ فَلْيَصُمْهُ وَمَنْ شَاءَ أَفْطَرَهُ»
'A'isha (Allah be pleased with her) reported that the Messenger of Allah ﷺ had ordered to observe fast (on 'Ashura) before the fasting in Ramadan was made obligatory. But when it became obligatory, then he who wished fasted on the day of Ashura, and he who wished did not observe it (on that day). (Using translation from Muslim 1125d)
كَانَ رَسُولُ اللهِ ﷺ «يَأْمُرُ بِصِيَامِ عَاشُورَاءَ قَبْلَ أَنْ يُفْرَضَ رَمَضَانُ فَلَمَّا فُرِضَ رَمَضَانُ كَانَ مَنْ شَاءَ صَامَ عَاشُورَاءَ وَمَنْ شَاءَ أَفْطَرَ»