Sunan Abi Dawud 2443
سنن أبي داود#2443Sahihحَدَّثَنَا مُسَدَّدٌ، حَدَّثَنَا يَحْيَى، عَنْ عُبَيْدِ اللَّهِ، قَالَ أَخْبَرَنِي نَافِعٌ، عَنِ ابْنِ عُمَرَ، قَالَ كَانَ عَاشُورَاءُ يَوْمًا نَصُومُهُ فِي الْجَاهِلِيَّةِ فَلَمَّا نَزَلَ رَمَضَانُ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " هَذَا يَوْمٌ مِنْ أَيَّامِ اللَّهِ فَمَنْ شَاءَ صَامَهُ وَمَنْ شَاءَ تَرَكَهُ " .
Ibn 'Umar said:'Ashurah was a day on which we used to fast in pre-Islamic days. When (fasting of) Ramadan was prescribed, the Messenger of Allah (ﷺ) said: This is one of the days of Allah ; he who wishes may fast on it
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:
In-book reference: 14:131