Hadith on Ashura: Recommendation to fast the day of Ashura, but not an obligation

Abdullah ibn Umar reported: During the time of ignorance, the people would fast the day of Ashura and the Messenger of Allah, peace and blessings be upon him, and the Muslims would fast as well until the fasting of Ramadan was made an obligation. Then the Prophet said, “Verily, Ashura is a day among the days of Allah, so whoever wishes to fast may do so and whoever wishes to break his fast may do so.”

Source: Sahih Muslim 1126

Grade: Sahih (authentic) according to Muslim

عَبْدُ اللَّهِ بْنُ عُمَرَ رَضِيَ اللَّهُ عَنْهُمَا أَنَّ أَهْلَ الْجَاهِلِيَّةِ كَانُوا يَصُومُونَ يَوْمَ عَاشُورَاءَ وَأَنَّ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ صَامَهُ وَالْمُسْلِمُونَ قَبْلَ أَنْ يُفْتَرَضَ رَمَضَانُ فَلَمَّا افْتُرِضَ رَمَضَانُ قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ إِنَّ عَاشُورَاءَ يَوْمٌ مِنْ أَيَّامِ اللَّهِ فَمَنْ شَاءَ صَامَهُ وَمَنْ شَاءَ تَرَكَهُ

1126 صحيح مسلم كِتَاب الصِّيَامِ من شاء فليصمه ومن شاء فليفطره