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.
muslim:1131bAḥmad b. al-Mundhir > Ḥammād b. Usāmah > Abū al-ʿUmays > Qays Fadhakar Bihadhā al-Isnād > And Zād > Abū Usāmah Faḥaddathanī Ṣadaqah b. Abū ʿImrān > Qays b. Muslim > Ṭāriq b. Shihāb > Abū Mūsá

You (only) observe fast on this day.  

مسلم:١١٣١bوَحَدَّثَنَاهُ أَحْمَدُ بْنُ الْمُنْذِرِ حَدَّثَنَا حَمَّادُ بْنُ أُسَامَةَ حَدَّثَنَا أَبُو الْعُمَيْسِ

أَخْبَرَنِي قَيْسٌ فَذَكَرَ بِهَذَا الإِسْنَادِ مِثْلَهُ وَزَادَ قَالَ أَبُو أُسَامَةَ فَحَدَّثَنِي صَدَقَةُ بْنُ أَبِي عِمْرَانَ عَنْ قَيْسِ بْنِ مُسْلِمٍ عَنْ طَارِقِ بْنِ شِهَابٍ عَنْ أَبِي مُوسَى ؓ قَالَ كَانَ أَهْلُ خَيْبَرَ يَصُومُونَ يَوْمَ عَاشُورَاءَ يَتَّخِذُونَهُ عِيدًا وَيُلْبِسُونَ نِسَاءَهُمْ فِيهِ حُلِيَّهُمْ وَشَارَتَهُمْ فَقَالَ رَسُولُ اللَّهِ ﷺ فَصُومُوهُ أَنْتُمْ