Quraish used to fast on the day of 'Ashura' in the Pre-Islamic period, and Messenger of Allah ﷺ too, used to fast on that day. When he came to Medina, he fasted on that day and ordered others to fast, too. Later when the fasting of the month of Ramadan was prescribed, he gave up fasting on the day of 'Ashura' and it became optional for one to fast on it or not.  

كَانَ يَوْمُ عَاشُورَاءَ تَصُومُهُ قُرَيْشٌ فِي الْجَاهِلِيَّةِ وَكَانَ رَسُولُ اللَّهِ ﷺ يَصُومُهُ فَلَمَّا قَدِمَ الْمَدِينَةَ صَامَهُ وَأَمَرَ بِصِيَامِهِ فَلَمَّا فُرِضَ رَمَضَانُ تَرَكَ يَوْمَ عَاشُورَاءَ فَمَنْ شَاءَ صَامَهُ وَمَنْ شَاءَ تَرَكَهُ  

'Ashura' (i.e. the tenth of Muharram) was a day on which the tribe of Quraish used to fast in the prelslamic period of ignorance. The Prophet ﷺ also used to fast on this day. So when he migrated to Medina, he fasted on it and ordered (the Muslims) to fast on it. When the fasting of Ramadan was enjoined, it became optional for the people to fast or not to fast on the day of Ashura.  

كَانَ عَاشُورَاءُ يَوْمًا تَصُومُهُ قُرَيْشٌ فِي الْجَاهِلِيَّةِ وَكَانَ النَّبِيُّ ﷺ يَصُومُهُ فَلَمَّا قَدِمَ الْمَدِينَةَ صَامَهُ وَأَمَرَ بِصِيَامِهِ فَلَمَّا نَزَلَ رَمَضَانُ كَانَ مَنْ شَاءَ صَامَهُ وَمَنْ شَاءَ لاَ يَصُومُهُ  

During the Pre-lslamic Period of ignorance the Quraish used to observe fasting on the day of 'Ashura', and the Prophet ﷺ himself used to observe fasting on it too. But when he came to Medina, he fasted on that day and ordered the Muslims to fast on it. When (the order of compulsory fasting in ) Ramadan was revealed, fasting in Ramadan became an obligation, and fasting on 'Ashura' was given up, and who ever wished to fast (on it) did so, and whoever did not wish to fast on it, did not fast.  

كَانَ يَوْمُ عَاشُورَاءَ تَصُومُهُ قُرَيْشٌ فِي الْجَاهِلِيَّةِ وَكَانَ النَّبِيُّ ﷺ يَصُومُهُ فَلَمَّا قَدِمَ الْمَدِينَةَ صَامَهُ وَأَمَرَ بِصِيَامِهِ فَلَمَّا نَزَلَ رَمَضَانُ كَانَ رَمَضَانُ الْفَرِيضَةَ وَتُرِكَ عَاشُورَاءُ فَكَانَ مَنْ شَاءَ صَامَهُ وَمَنْ شَاءَ لَمْ يَصُمْهُ  

The Quraish used to fast on the day of 'Ashurah in pre Islamic days. The Messenger of Allah ﷺ would fast on it in pre-Islamic period. When the Messenger of Allah ﷺ came to Medina, he fasted on it and commanded to fast on it. When the fast of Ramadan was prescribed, that became obligatory, and (fasting on) 'Ashurah was abandoned. He who wishes may fast on it and he who wishes may leave it.  

كَانَ يَوْمُ عَاشُورَاءَ يَوْمًا تَصُومُهُ قُرَيْشٌ فِي الْجَاهِلِيَّةِ وَكَانَ رَسُولُ اللَّهِ ﷺ يَصُومُهُ فِي الْجَاهِلِيَّةِ فَلَمَّا قَدِمَ رَسُولُ اللَّهِ ﷺ الْمَدِينَةَ صَامَهُ وَأَمَرَ بِصِيَامِهِ فَلَمَّا فُرِضَ رَمَضَانُ كَانَ هُوَ الْفَرِيضَةَ وَتُرِكَ عَاشُورَاءُ فَمَنْ شَاءَ صَامَهُ وَمَنْ شَاءَ تَرَكَهُ  

Yahya related to me from Malik from Hisham ibn Urwa from his father that A'isha, the wife of the Prophet ﷺ said, "The day of Ashura was a day the Quraysh used to fast in the jahiliyya, and the Messenger of Allah ﷺ used also to fast it during the jahiliyya. Then when the Messenger of Allah ﷺ came to Madina he fasted it and ordered that it be fasted. Then Ramadan was made obligatory, and that became the fard instead of Ashura, but whoever wanted to, fasted it, and whoever did not want to, did not fast it."  

عَنْ عَائِشَةَ زَوْجِ النَّبِيِّ ﷺ أَنَّهَا قَالَتْ كَانَ يَوْمُ عَاشُورَاءَ يَوْمًا تَصُومُهُ قُرَيْشٌ فِي الْجَاهِلِيَّةِ وَكَانَ رَسُولُ اللَّهِ ﷺ يَصُومُهُ فِي الْجَاهِلِيَّةِ فَلَمَّا قَدِمَ رَسُولُ اللَّهِ ﷺ الْمَدِينَةَ صَامَهُ وَأَمَرَ بِصِيَامِهِ فَلَمَّا فُرِضَ رَمَضَانُ كَانَ هُوَ الْفَرِيضَةَ وَتُرِكَ يَوْمُ عَاشُورَاءَ فَمَنْ شَاءَ صَامَهُ وَمَنْ شَاءَ تَرَكَهُ  

During the Pre-lslamic Period of ignorance the Quraish used to observe fasting on the day of 'Ashura', and the Prophet ﷺ himself used to observe fasting on it too. But when he came to Medina, he fasted on that day and ordered the Muslims to fast on it. When (the order of compulsory fasting in ) Ramadan was revealed, fasting in Ramadan became an obligation, and fasting on 'Ashura' was given up, and who ever wished to fast (on it) did so, and whoever did not wish to fast on it, did not fast. (Using translation from Bukhārī 4504)  

كَانَ يَوْمُ عَاشُورَاءَ يَوْمًا تَصُومُهُ قُرَيْشٌ فِي الْجَاهِلِيَّةِ وَكَانَ رَسُولُ اللهِ ﷺ يَصُومُهُ فَلَمَّا قَدِمَ الْمَدِينَةَ صَامَهُوَأَمَرَ بِصِيَامِهِ فَلَمَّا نَزَلَ صَوْمُ رَمَضَانَ كَانَ رَمَضَانُ هُوَ الْفَرِيضَةَ وَتَرَكَ عَاشُورَاءَ فَكَانَ مَنْ شَاءَ صَامَهُ وَمَنْ شَاءَ لَمْ يَصُمْهُ  

The Quraish used to fast on the day of 'Ashurah in pre Islamic days. The Messenger of Allah ﷺ would fast on it in pre-Islamic period. When the Messenger of Allah ﷺ came to Medina, he fasted on it and commanded to fast on it. When the fast of Ramadan was prescribed, that became obligatory, and (fasting on) 'Ashurah was abandoned. He who wishes may fast on it and he who wishes may leave it. (Using translation from Abū Dāʾūd 2442)   

كَانَ يَوْمُ عَاشُورَاءَ يَوْمًا يَصُومُهُ قُرَيْشٌ فِي الْجَاهِلِيَّةِ وَكَانَ رَسُولُ اللهِ ﷺ يَصُومُهُ فَلَمَّا قَدِمَ الْمَدِينَةَ صَامَهُ وَأَمَرَ بِصِيَامِهِ فَلَمَّا نَزَلَتْ فَرِيضَةُ شَهْرِ رَمَضَانَ كَانَ رَمَضَانُ هُوَ الَّذِي يَصُومُهُ وَتَرَكَ يَوْمَ عَاشُورَاءَ فَمَنْ شَاءَ صَامَهُ وَمَنْ شَاءَ أَفْطَرَهُ  

The Quraish used to fast on the day of 'Ashurah in pre Islamic days. The Messenger of Allah ﷺ would fast on it in pre-Islamic period. When the Messenger of Allah ﷺ came to Medina, he fasted on it and commanded to fast on it. When the fast of Ramadan was prescribed, that became obligatory, and (fasting on) 'Ashurah was abandoned. He who wishes may fast on it and he who wishes may leave it. (Using translation from Abū Dāʾūd 2442)   

كَانَ يَوْمُ عَاشُورَاءَ يَوْمًا يَصُومُهُ رَسُولُ اللهِ ﷺ فِي الْجَاهِلِيَّةِ وَكَانَتْ قُرَيْشٌ تَصُومُهُ فِي الْجَاهِلِيَّةِ فَلَمَّا قَدِمَ النَّبِيُّ ﷺ الْمَدِينَةَ صَامَهُ وَأَمَرَ بِصِيَامِهِ فَلَمَّا نَزَلَ رَمَضَانُ كَانَ رَمَضَانُ هُوَ الْفَرِيضَةَ وَتَرَكَ عَاشُورَاءَ  

The Quraish used to fast on the day of 'Ashurah in pre Islamic days. The Messenger of Allah ﷺ would fast on it in pre-Islamic period. When the Messenger of Allah ﷺ came to Medina, he fasted on it and commanded to fast on it. When the fast of Ramadan was prescribed, that became obligatory, and (fasting on) 'Ashurah was abandoned. He who wishes may fast on it and he who wishes may leave it. (Using translation from Abū Dāʾūd 2442)   

«كَانَ يَوْمُ عَاشُورَاءَ يَوْمًا تَصُومُهُ قُرَيْشٌ فِي الْجَاهِلِيَّةِ فَلَمَّا قَدِمَ رَسُولُ اللَّهِ ﷺ الْمَدِينَةَ صَامَهُ وَأَمَرَ بِصِيَامِهِ حَتَّى إِذَا فُرِضَ رَمَضَانُ كَانَ رَمَضَانُ هُوَ الْفَرِيضَةُ وَتُرِكَ يَوْمُ عَاشُورَاءَ فَمَنْ شَاءَ صَامَهُ وَمَنْ شَاءَ تَرَكَهُ»  

The Quraish used to fast on the day of 'Ashurah in pre Islamic days. The Messenger of Allah ﷺ would fast on it in pre-Islamic period. When the Messenger of Allah ﷺ came to Medina, he fasted on it and commanded to fast on it. When the fast of Ramadan was prescribed, that became obligatory, and (fasting on) 'Ashurah was abandoned. He who wishes may fast on it and he who wishes may leave it. (Using translation from Abū Dāʾūd 2442)   

أَنَّهَا قَالَتْ «كَانَ يَوْمُ عَاشُورَاءَ يَوْمًا تَصُومُهُ قُرَيْشٌ فِي الْجَاهِلِيَّةِ فَلَمَّا قَدِمَ رَسُولُ اللَّهِ ﷺ الْمَدِينَةَ صَامَهُ وَأَمَرَ بِصِيَامِهِ فَلَمَّا فُرِضَ رَمَضَانُ كَانَ هُوَ الْفَرِيضَةَ وَتُرِكَ يَوْمُ عَاشُورَاءَ فَمَنْ شَاءَ صَامَ وَمَنْ شَاءَ تَرَكَهُ»  

The Quraish used to fast on the day of 'Ashurah in pre Islamic days. The Messenger of Allah ﷺ would fast on it in pre-Islamic period. When the Messenger of Allah ﷺ came to Medina, he fasted on it and commanded to fast on it. When the fast of Ramadan was prescribed, that became obligatory, and (fasting on) 'Ashurah was abandoned. He who wishes may fast on it and he who wishes may leave it. (Using translation from Abū Dāʾūd 2442)   

«كَانَ يَوْمُ عَاشُورَاءَ يَوْمًا تَصُومُهُ قُرَيْشٌ فِي الْجَاهِلِيَّةِ وَكَانَ رَسُولُ اللهِ ﷺ يَصُومُهُ فَلَمَّا قَدِمَ الْمَدِينَةَ صَامَهُ وَأَمَرَ بِصِيَامِهِ فَنَزَلَ صَوْمُ رَمَضَانَ فَكَانَ رَمَضَانُ هُوَ الْفَرِيضَةُ فَمَنْ شَاءَ صَامَ يَوْمَ عَاشُورَاءَ وَمَنْ شَاءَ تَرَكَ»  

The Quraish used to fast on the day of 'Ashurah in pre Islamic days. The Messenger of Allah ﷺ would fast on it in pre-Islamic period. When the Messenger of Allah ﷺ came to Medina, he fasted on it and commanded to fast on it. When the fast of Ramadan was prescribed, that became obligatory, and (fasting on) 'Ashurah was abandoned. He who wishes may fast on it and he who wishes may leave it. (Using translation from Abū Dāʾūd 2442)   

كَانَ يَوْمُ عَاشُورَاءَ يَوْمًا تَصُومُهُ قُرَيْشٌ فِي الْجَاهِلِيَّةِ فَكَانَ رَسُولُ اللهِ ﷺ «يَصُومُهُ فَلَمَّا قَدِمَ الْمَدِينَةَ صَامَهُ وَأَمَرَ بِصِيَامِهِ» فَنَزَلَ صَوْمُ رَمَضَانَ فَكَانَ رَمَضَانُ هُوَ الْفَرِيضَةَ فَمَنْ شَاءَ صَامَ يَعْنِي عَاشُورَاءَ وَمَنْ شَاءَ تَرَكَ  

[Machine] The day of Ashura used to be observed as a fast by the Quraysh in the pre-Islamic era, and the Prophet Muhammad ﷺ also used to fast on this day during that time. When the Prophet Muhammad ﷺ arrived in Madinah, he continued to fast on this day and ordered others to also observe the fast. However, when the obligatory fast of Ramadan was established, it became the main priority, and the fast of Ashura was left as optional. So, whoever wishes to fast on this day may do so, and whoever wishes to leave it may do so.  

كَانَ يَوْمُ عَاشُورَاءَ يَوْمًا تَصُومُهُ قُرَيْشٌ فِي الْجَاهِلِيَّةِ وَكَانَ رَسُولُ اللهِ ﷺ يَصُومُهُ فِي الْجَاهِلِيَّةِ فَلَمَّا قَدِمَ رَسُولُ اللهِ ﷺ الْمَدِينَةَ صَامَهُ وَأَمَرَ بِصِيَامِهِ فَلَمَّا فُرِضَ رَمَضَانُ كَانَ هُوَ الْفَرِيضَةُ وَتَرَكَ يَوْمَ عَاشُورَاءَ فَمَنْ شَاءَ صَامَهُ وَمَنْ شَاءَ تَرَكَهُ