Sahih Muslim Book - 13, Hadith - 2637

حَدَّثَنَا زُهَيْرُ بْنُ حَرْبٍ حَدَّثَنَا جَرِيرٌ عَنْ هِشَامِ بْنِ عُرْوَةَ عَنْ أَبِيهِ عَنْ عَائِشَةَ - رضى الله عنها - قَالَتْ كَانَتْ قُرَيْشٌ تَصُومُ عَاشُورَاءَ فِى الْجَاهِلِيَّةِ وَكَانَ رَسُولُ اللَّهِ -صلى الله عليه وسلم- يَصُومُهُ فَلَمَّا هَاجَرَ إِلَى الْمَدِينَةِ صَامَهُ وَأَمَرَ بِصِيَامِهِ فَلَمَّا فُرِضَ شَهْرُ رَمَضَانَ قَالَ « مَنْ شَاءَ صَامَهُ وَمَنْ شَاءَ تَرَكَهُ ».

It was narrated that Aishah [may Allah be pleased with her] said: “The Quraish used to fast on Ashura during the Jahiliyyah, and the Messenger of Allah (SAW) used fast on (that day) too. When he immigrated to Al-Madinah, he fasted this day and ordered that this fast be observed. When (fasting during) during the Month of Ramadan was enjoined, he said: ‘Whoever wishes may fast it (this day) and whoever wishes may forsake it.’”