حَدَّثَنِي يَعْقُوبُ بْنُ إِبْرَاهِيمَ، حَدَّثَنَا رَوْحٌ، حَدَّثَنَا شُعْبَةُ، حَدَّثَنَا أَبُو بِشْرٍ، عَنْ سَعِيدِ بْنِ جُبَيْرٍ، عَنِ ابْنِ عَبَّاسٍ ـ رضى الله عنهما ـ قَالَ لَمَّا قَدِمَ رَسُولُ اللَّهِ صلى الله عليه وسلم الْمَدِينَةَ، وَالْيَهُودُ تَصُومُ عَاشُورَاءَ، فَسَأَلَهُمْ، فَقَالُوا هَذَا الْيَوْمُ الَّذِي ظَهَرَ فِيهِ مُوسَى عَلَى فِرْعَوْنَ، فَقَالَ النَّبِيُّ صلى الله عليه وسلم " نَحْنُ أَوْلَى بِمُوسَى مِنْهُمْ فَصُومُوهُ ".
Narrated Ibn `Abbas: When Allah's Messenger (PBUH) arrived at Medina, he found the Jews observing the fast on the day of 'Ashura' (10th of Muharram). The Prophet (PBUH) asked them (about it) and they replied, "This is the day when Moses became victorious over Pharaoh." The Prophet (PBUH) said (to the Muslims), "We are nearer to Moses than they, so fast on this day." Translation Not Available
Book Ref: Sahih Bukhari Book 65 Hadith 4737
Web Ref: Sahih Bukhari Vol 6 Book 60 Hadith 261