Ibn Umar reported: The Messenger of Allah, peace and blessings be upon him, said, “Verily, ‘Ashura is one of the days of Allah. Whoever wants to fast may do so, and whoever does not want to fast may do so.”
Source: Ṣaḥīḥ Muslim 1126
Grade: Sahih (authentic) according to Muslim
عَنْ ابْنِ عُمَرَ أَنَّ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ إِنَّ عَاشُورَاءَ يَوْمٌ مِنْ أَيَّامِ اللَّهِ فَمَنْ شَاءَ صَامَهُ وَمَنْ شَاءَ تَرَكَهُ
1126 صحيح مسلم كتاب الصيام باب صوم يوم عاشوراء
