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.
tabarani:16947Muḥammad b. al-Layth al-Jawharī > Muḥammad b. Sulaymān Lūwayn > Abū Maʿshar al-Barāʾ > ʿAbdullāh b. Abū ʿUthmān > Ayyūb b. ʿAbdullāh b. Yasār > Muʿāwiyah / Bimakkah al-Mukarramah Yawm ʿĀshūrāʾ

[Machine] I heard Muawiyah, while he was in Makkah Al-Mukarramah, on the day of Ashura, saying, "The Messenger of Allah ﷺ used to fast it and he said, 'Whoever among you did not f ast it, then let him fast it.'"  

الطبراني:١٦٩٤٧حَدَّثَنَا مُحَمَّدُ بْنُ اللَّيْثِ الْجَوْهَرِيُّ ثنا مُحَمَّدُ بْنُ سُلَيْمَانَ لُوَيْنُ ثنا أَبُو مَعْشَرٍ الْبَرَاءُ ثنا عَبْدُ اللهِ بْنُ أَبِي عُثْمَانَ ثنا أَيُّوبُ بْنُ عَبْدِ اللهِ بْنِ يَسَارٍ قَالَ

سَمِعْتُ مُعَاوِيَةَ وَهُوَ بِمَكَّةَ الْمُكَرَّمَةِ يَوْمَ عَاشُورَاءَ يَقُولُ صَامَهُ رَسُولُ اللهِ ﷺ وَقَالَ «مَنْ لَمْ يَكُنْ صَامَ مِنْكُمْ فَلْيَصُمْهُ»