كتاب الصيام
13
The Book of Fasting
(19)
Chapter: Fasting on the day of Ashura'
(19)
باب صَوْمِ يَوْمِ عَاشُورَاءَ ‏‏
Sahih Muslim 1125 b

This hadith is narrated on the authority of Hisham with the same chain of transmitters, but he made no mention in the first part of the hadith that the Messenger of Allah (ﷺ) used to observe fast, and said about the second part that he abandoned the (fast) of Ashura, and he who wished observed the fast and who wished otherwise abandoned it, and he did not hold it as the words of the Messenger of Allah (ﷺ) as mentioned in the narration transmitted by Jarir.

وَحَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، وَأَبُو كُرَيْبٍ قَالاَ حَدَّثَنَا ابْنُ نُمَيْرٍ، عَنْ هِشَامٍ، بِهَذَا الإِسْنَادِ وَلَمْ يَذْكُرْ فِي أَوَّلِ الْحَدِيثِ وَكَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم يَصُومُهُ ‏.‏ وَقَالَ فِي آخِرِ الْحَدِيثِ وَتَرَكَ عَاشُورَاءَ فَمَنْ شَاءَ صَامَهُ وَمَنْ شَاءَ تَرَكَهُ ‏.‏ وَلَمْ يَجْعَلْهُ مِنْ قَوْلِ النَّبِيِّ صلى الله عليه وسلم كَرِوَايَةِ جَرِيرٍ ‏.‏
Reference : Sahih Muslim 1125 b
In-book reference : Book 13, Hadith 144
USC-MSA web (English) reference : Book 6, Hadith 2500
  (deprecated numbering scheme)