Sahih Muslim Book - 13, Hadith - 2645

حَدَّثَنَا أَبُو كُرَيْبٍ حَدَّثَنَا أَبُو أُسَامَةَ عَنِ الْوَلِيدِ - يَعْنِى ابْنَ كَثِيرٍ - حَدَّثَنِى نَافِعٌ أَنَّ عَبْدَ اللَّهِ بْنَ عُمَرَ - رضى الله عنهما - حَدَّثَهُ أَنَّهُ سَمِعَ رَسُولَ اللَّهِ -صلى الله عليه وسلم- يَقُولُ فِى يَوْمِ عَاشُورَاءَ « إِنَّ هَذَا يَوْمٌ كَانَ يَصُومُهُ أَهْلُ الْجَاهِلِيَّةِ فَمَنْ أَحَبَّ أَنْ يَصُومَهُ فَلْيَصُمْهُ وَمَنْ أَحَبَّ أَنْ يَتْرُكَهُ فَلْيَتْرُكْهُ ». وَكَانَ عَبْدُ اللَّهِ - رضى الله عنه - لاَ يَصُومُهُ إِلاَّ أَنْ يُوَافِقَ صِيَامَهُ.

Abdullah bin Umar [may Allah be pleased with them] narrated that he heard the Messenger of Allah (SAW) say concerning the day of Ashura: “This day was fasted by the people of Jahiliyyah, so whoever wants to fast it, let him do so, and whoever wants to leave it , let him do so.” Abdullah [may Allah be pleased with them] would not fast it, except when it coincides with a day that he usually fasted.