وَحَدَّثَنِي ابْنُ أَبِي عُمَرَ، حَدَّثَنَا سُفْيَانُ، عَنْ أَيُّوبَ، عَنْ عَبْدِ اللَّهِ بْنِ سَعِيدِ بْنِ جُبَيْرٍ، عَنْ أَبِيهِ، عَنِ ابْنِ عَبَّاسٍ، - رضى الله عنهما - أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَدِمَ الْمَدِينَةَ فَوَجَدَ الْيَهُودَ صِيَامًا يَوْمَ عَاشُورَاءَ فَقَالَ لَهُمْ رَسُولُ اللَّهِ صلى الله عليه وسلم " مَا هَذَا الْيَوْمُ الَّذِي تَصُومُونَهُ " . فَقَالُوا هَذَا يَوْمٌ عَظِيمٌ أَنْجَى اللَّهُ فِيهِ مُوسَى وَقَوْمَهُ وَغَرَّقَ فِرْعَوْنَ وَقَوْمَهُ فَصَامَهُ مُوسَى شُكْرًا فَنَحْنُ نَصُومُهُ . فَقَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " فَنَحْنُ أَحَقُّ وَأَوْلَى بِمُوسَى مِنْكُمْ " . فَصَامَهُ رَسُولُ اللَّهِ صلى الله عليه وسلم وَأَمَرَ بِصِيَامِهِ .
What is the (significance) of this day that you observe fast on it? They said: It is the day of great (significance) when Allah delivered Moses and his people, and drowned the Pharaoh and his people, and Moses observed fast out of gratitude and we also observe it. Upon this the Messenger of Allah (ﷺ) said: We have more right, and we have a closer connection with Moses than you have; so Allah's Messenger (ﷺ) observed fast (on the day of 'Ashura), and gave orders that it should be observed.
Source: Sahih Muslim — repository translation · Imam Muslim ibn al-Hajjaj al-Naysaburi — authenticity/grade metadata requires independent source review · Sunnah.comAudio not available for the selected reciter.
Source: Sahih Muslim — repository arabic · Imam Muslim ibn al-Hajjaj al-Naysaburi · Sunnah.com