Sahih Muslim 2660
صحيح مسلم#2660Sahihوَحَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، وَابْنُ، نُمَيْرٍ قَالاَ حَدَّثَنَا أَبُو أُسَامَةَ، عَنْ أَبِي عُمَيْسٍ، عَنْ قَيْسِ بْنِ مُسْلِمٍ، عَنْ طَارِقِ بْنِ شِهَابٍ، عَنْ أَبِي مُوسَى، - رضى الله عنه - قَالَ كَانَ يَوْمُ عَاشُورَاءَ يَوْمًا تُعَظِّمُهُ الْيَهُودُ وَتَتَّخِذُهُ عِيدًا فَقَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " صُومُوهُ أَنْتُمْ " .
Abu Musa (Allah be pleased with him) reported:The day of 'Ashura was one which the Jews respected and they treated it as Id. The Messenger of Allah (ﷺ) said: You also observe fast on this day
Scholarly Authentication
The label above is the grade most of these scholars gave — one dissenting opinion no longer speaks for all of them. If any scholar calls a narration fabricated, that verdict is shown instead, whatever the others say. Each scholar's own wording:
Every narration in Sahih Muslim is accepted as Sahih (authentic) by the established status of the book.
In-book reference: 13:166