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
nasai-kubra:2692 – Qutaybah b. Saʿīd > Sufyān > al-Zuhrī > Ḥumayd b. ʿAbd al-Raḥman b. ʿAwf > Muʿāwiyah Yawm ʿĀshūrāʾ / > al-Minbar > Yā Ahl al-Madīnah Ayn ʿUlamāʾukum Yā Ahl al-Madīnah

"I heard Mu'awiyah say on the day of 'Ashura when he was on the Mindar: O people of Al-Madinah, where are your scholars? I heard the Messenger of Allah say on this day: "I am fasting, so whoever wants to fast let him do so." (Using translation from Nasāʾī 2371)  

الكبرى للنسائي:٢٦٩٢ – أَخْبَرَنَا قُتَيْبَةُ بْنُ سَعِيدٍ قَالَ حَدَّثَنَا سُفْيَانُ عَنِ الزُّهْرِيِّ عَنْ حُمَيْدِ بْنِ عَبْدِ الرَّحْمَنِ بْنِ عَوْفٍ قَالَ

سَمِعْتُ مُعَاوِيَةَ يَوْمَ عَاشُورَاءَ وَهُوَ عَلَى الْمِنْبَرِ يَقُولُ يَا أَهْلَ الْمَدِينَةِ أَيْنَ عُلَمَاؤُكُمْ يَا أَهْلَ الْمَدِينَةِ سَمِعْتُ رَسُولَ اللهِ ﷺ يَقُولُ فِي هَذَا الْيَوْمِ «إِنِّي صَائِمٌ فَمَنْ شَاءَ أَنْ يَصُومَ فَلْيَصُمْ»  

See similar narrations below:

Collected by Nasāʾī
nasai:2371 – Qutaybah > Sufyān > al-Zuhrī > Ḥumayd b. ʿAbd al-Raḥman b. ʿAwf > Muʿāwiyah Yawm ʿĀshūrāʾ / > al-Minbar > Yā Ahl al-Madīnah Ayn ʿUlamāʾukum

"I heard Mu'awiyah say on the day of 'Ashura when he was on the Mindar: O people of Al-Madinah, where are your scholars? I heard the Messenger of Allah say on this day: "I am fasting, so whoever wants to fast let him do so."  

النسائي:٢٣٧١ – أَخْبَرَنَا قُتَيْبَةُ عَنْ سُفْيَانَ عَنِ الزُّهْرِيِّ عَنْ حُمَيْدِ بْنِ عَبْدِ الرَّحْمَنِ بْنِ عَوْفٍ قَالَ

سَمِعْتُ مُعَاوِيَةَ يَوْمَ عَاشُورَاءَ وَهُوَ عَلَى الْمِنْبَرِ يَقُولُ يَا أَهْلَ الْمَدِينَةِ أَيْنَ عُلَمَاؤُكُمْ سَمِعْتُ رَسُولَ اللَّهِ ﷺ يَقُولُ فِي هَذَا الْيَوْمِ إِنِّي صَائِمٌ فَمَنْ شَاءَ أَنْ يَصُومَ فَلْيَصُمْ