Sahih al-Bukhari 63:167
Narrated Ibn `Abbas:
When the Prophet (ﷺ) arrived at Medina he found that the Jews observed fast on the day of 'Ashura'. They were asked the reason for the fast. They replied, "This is the day when Allah caused Moses and the children of Israel to have victory over Pharaoh, so we fast on this day as a sign of glorifying it." Allah's Messenger (ﷺ) said, "We are closer to Moses than you." Then he ordered that fasting on this day should be observed.
Reference
Sahih al-Bukhari 63:167
In-book reference
Book 63, Hadith 167
Arabic Text
حَدَّثَنَا زِيَادُ بْنُ أَيُّوبَ، حَدَّثَنَا هُشَيْمٌ، حَدَّثَنَا أَبُو بِشْرٍ، عَنْ سَعِيدِ بْنِ جُبَيْرٍ، عَنِ ابْنِ عَبَّاسٍ ـ رضى الله عنهما ـ قَالَ لَمَّا قَدِمَ النَّبِيُّ صلى الله عليه وسلم الْمَدِينَةَ وَجَدَ الْيَهُودَ يَصُومُونَ عَاشُورَاءَ، فَسُئِلُوا عَنْ ذَلِكَ، فَقَالُوا هَذَا الْيَوْمُ الَّذِي أَظْفَرَ اللَّهُ فِيهِ مُوسَى وَبَنِي إِسْرَائِيلَ عَلَى فِرْعَوْنَ، وَنَحْنُ نَصُومُهُ تَعْظِيمًا لَهُ، فَقَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " نَحْنُ أَوْلَى بِمُوسَى مِنْكُمْ ". ثُمَّ أَمَرَ بِصَوْمِهِ.