Caution: Translations of Quran and Ḥadīth may lead to possible misapplications and misinterpretations. This site is intended for students of sacred knowledge that are proficient in comprehending classical Arabic and have a strong foundation in Islamic sciences. Also note that religious injunctions rely on several aspects beyond what one may glean through reading individual aḥādīth.
Qurʾān Bukhārī Muslim Nasāʾī Abū Dāwūd Tirmidhī Ibn Mājah Mālik Aḥmad Dārimī Ḥākim Ibn Ḥibbān Ṭabarānī Nasāʾī's Kubrá Bayhaqī al-Luʾluʾ wa-al-Marjān Ibn Rajab's Fifty Riyāḍ al-Ṣāliḥīn Aḥmad's Zuhd Suyūṭī
bukhari:2005 – ʿAlī b. ʿAbdullāh > Abū Usāmah > Abū ʿUmays > Qays b. Muslim > Ṭāriq b. Shihāb > Abū Mūsá

The day of 'Ashura' was considered as ʿId day by the Jews. So the Prophet ﷺ ordered, "I recommend you (Muslims) to fast on this day."  

البخاري:٢٠٠٥ – حَدَّثَنَا عَلِيُّ بْنُ عَبْدِ اللَّهِ حَدَّثَنَا أَبُو أُسَامَةَ عَنْ أَبِي عُمَيْسٍ عَنْ قَيْسِ بْنِ مُسْلِمٍ عَنْ طَارِقِ بْنِ شِهَابٍ عَنْ أَبِي مُوسَى ؓ قَالَ

كَانَ يَوْمُ عَاشُورَاءَ تَعُدُّهُ الْيَهُودُ عِيدًا قَالَ النَّبِيُّ ﷺ فَصُومُوهُ أَنْتُمْ  

See similar narrations below:

Collected by Muslim, Aḥmad
muslim:1131a – Abū Bakr b. Abū Shaybah And Ibn Numayr > Abū Usāmah > Abū ʿUmays > Qays b. Muslim > Ṭāriq b. Shihāb > Abū Mūsá

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.  

مسلم:١١٣١a – وَحَدَّثَنَا 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 ؓ قَالَ

كَانَ يَوْمُ عَاشُورَاءَ يَوْمًا تُعَظِّمُهُ الْيَهُودُ وَتَتَّخِذُهُ عِيدًا فَقَالَ رَسُولُ اللَّهِ ﷺ صُومُوهُ أَنْتُمْ  

ahmad:19669 – Abū Usāmah > Abū al-ʿUmays > Qays b. Muslim > Ṭāriq b. Shihāb > Abū Mūsá

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. (Using translation from Muslim 1131a)  

أحمد:١٩٦٦٩ – حَدَّثَنَا أَبُو أُسَامَةَ حَدَّثَنِي أَبُو الْعُمَيْسِ عَنْ قَيْسِ بْنِ مُسْلِمٍ عَنْ طَارِقِ بْنِ شِهَابٍ عَنْ أَبِي مُوسَى قَالَ

كَانَ يَوْمُ عَاشُورَاءَ يَوْمًا تَصُومُهُ الْيَهُودُ تَتَّخِذُهُ عِيدًا فَقَالَ رَسُولُ اللهِ ﷺ صُومُوهُ أَنْتُمْ