The Book of Fasting
13/19. Chapter:
Fasting on the day of Ashura'
Sahih Muslim
وَحَدَّثَنَا ابْنُ أَبِي عُمَرَ، حَدَّثَنَا سُفْيَانُ بْنُ عُيَيْنَةَ، عَنِ الزُّهْرِيِّ، بِهَذَا الإِسْنَادِ سَمِعَ النَّبِيَّ صلى الله عليه وسلم يَقُولُ فِي مِثْلِ هَذَا الْيَوْمِ " إِنِّي صَائِمٌ فَمَنْ شَاءَ أَنْ يَصُومَ فَلْيَصُمْ " . وَلَمْ يَذْكُرْ بَاقِيَ حَدِيثِ مَالِكٍ وَيُونُسَ .
This hadith has been narrated on the authority of Zuhri with the same chain of transmitters that be heard Allah's Apostle (ﷺ) as saying on a similar day: I am fasting today, so he who wishes to observe fast should do so; but he did not make mention of the rest of the hadith.
Reference : Sahih Muslim 1129cIn-book reference : Book 13, Hadith 161USC-MSA web (English) reference : Book 6, Hadith 2517