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muslim:1135 – Qutaybah b. Saʿīd > Ḥātim / Ibn Ismāʿīl > Yazīd b. Abū ʿUbayd > Salamah b. al-Akwaʿ

Salama b. al-Akwa' (Allah be pleased with him) reported that the Messenger of Allah ﷺ sent a person of the tribe of Aslam on the day of 'Ashura and commanded him to declare to the people to observe fast in case they had not observed it, and to complete fast till evening if they had taken food  

مسلم:١١٣٥ – حَدَّثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ حَدَّثَنَا حَاتِمٌ يَعْنِي ابْنَ إِسْمَاعِيلَ عَنْ يَزِيدَ بْنِ أَبِي عُبَيْدٍ عَنْ سَلَمَةَ بْنِ الأَكْوَعِ ؓ

أَنَّهُ قَالَ بَعَثَ رَسُولُ اللَّهِ ﷺ رَجُلاً مِنْ أَسْلَمَ يَوْمَ عَاشُورَاءَ فَأَمَرَهُ أَنْ يُؤَذِّنَ فِي النَّاسِ مَنْ كَانَ لَمْ يَصُمْ فَلْيَصُمْ وَمَنْ كَانَ أَكَلَ فَلْيُتِمَّ صِيَامَهُ إِلَى اللَّيْلِ  

See similar narrations below:

Collected by Bukhārī, Aḥmad, Ibn Ḥibbān
bukhari:2007 – al-Makkī b. Ibrāhīm > Yazīd > Salamah b. al-Akwaʿ

The Prophet ﷺ ordered a man from the tribe of Bani Aslam to announce amongst the people that whoever had eaten should fast the rest of the day, and whoever had not eaten should continue his fast, as that day was the day of 'Ashura' .  

البخاري:٢٠٠٧ – حَدَّثَنَا الْمَكِّيُّ بْنُ إِبْرَاهِيمَ حَدَّثَنَا يَزِيدُ عَنْ سَلَمَةَ بْنِ الأَكْوَعِ ؓ قَالَ

أَمَرَ النَّبِيُّ ﷺ رَجُلاً مِنْ أَسْلَمَ أَنْ أَذِّنْ فِي النَّاسِ أَنَّ مَنْ كَانَ أَكَلَ فَلْيَصُمْ بَقِيَّةَ يَوْمِهِ وَمَنْ لَمْ يَكُنْ أَكَلَ فَلْيَصُمْ فَإِنَّ الْيَوْمَ يَوْمُ عَاشُورَاءَ  

bukhari:7265 – Musaddad > Yaḥyá > Yazīd b. Abū ʿUbayd > Salamah b. al-Akwaʿ

Messenger of Allah ﷺ said to a man from the tribe of Al-Aslam, "Proclaim among your people (or the people) on the day of 'Ashura' (tenth of Muharram), 'Whosoever has eaten anything should fast for the rest of the day; and whoever has not eaten anything, should complete his fast.' "  

البخاري:٧٢٦٥ – حَدَّثَنَا مُسَدَّدٌ حَدَّثَنَا يَحْيَى عَنْ يَزِيدَ بْنِ أَبِي عُبَيْدٍ حَدَّثَنَا سَلَمَةُ بْنُ الأَكْوَعِ

أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ لِرَجُلٍ مِنْ أَسْلَمَ أَذِّنْ فِي قَوْمِكَ أَوْ فِي النَّاسِ يَوْمَ عَاشُورَاءَ أَنَّ مَنْ أَكَلَ فَلْيُتِمَّ بَقِيَّةَ يَوْمِهِ وَمَنْ لَمْ يَكُنْ أَكَلَ فَلْيَصُمْ  

ahmad:16507 – Ḥammād b. Masʿadah > Yazīd / Ibn Abū ʿUbaydʿan Salamah b. al-Akwaʿ

[Machine] "The Prophet ﷺ ordered a man who embraced Islam to give the call to prayer among the people on the day of Ashura. Whoever was fasting, let him complete his fast, and whoever had eaten, let him not eat anything and complete his fast."  

أحمد:١٦٥٠٧ – حَدَّثَنَا حَمَّادُ بْنُ مَسْعَدَةَ عَنْ يَزِيدَ يَعْنِي ابْنَ أَبِي عُبَيْدٍعَنْ سَلَمَةَ بْنِ الْأَكْوَعِ

أَنَّ النَّبِيَّ ﷺ أَمَرَ رَجُلًا مِنْ أَسْلَمَ أَنْ يُؤَذِّنَ فِي النَّاسِ يَوْمَ عَاشُورَاءَ مَنْ كَانَ صَائِمًا فَلْيُتِمَّ صَوْمَهُ وَمَنْ كَانَ أَكَلَ فَلَا يَأْكُلْ شَيْئًا وَلِيُتِمَّ صَوْمَهُ  

ahmad:16526 – Yaḥyá b. Saʿīd > Yazīd b. Abū ʿUbayd > Salamah b. al-Akwaʿ

Messenger of Allah ﷺ said to a man from the tribe of Al-Aslam, "Proclaim among your people (or the people) on the day of 'Ashura' (tenth of Muharram), 'Whosoever has eaten anything should fast for the rest of the day; and whoever has not eaten anything, should complete his fast.' " (Using translation from Bukhārī 7265)  

أحمد:١٦٥٢٦ – حَدَّثَنَا يَحْيَى بْنُ سَعِيدٍ عَنْ يَزِيدَ بْنِ أَبِي عُبَيْدٍ قَالَ حَدَّثَنَا سَلَمَةُ بْنُ الْأَكْوَعِ

أَنَّ رَسُولَ اللهِ ﷺ قَالَ لِرَجُلٍ مِنْ أَسْلَمَ أَذِّنْ فِي قَوْمِكَ أَوْ فِي النَّاسِ يَوْمَ عَاشُورَاءَ مَنْ أَكَلَ فَلْيَصُمْ بَقِيَّةَ يَوْمِهِ وَمَنْ لَمْ يَكُنْ أَكَلَ فَلْيَصُمْ  

ذِكْرُ الْأَمْرِ بِصَوْمِ بَعْضِ الْيَوْمِ مِنْ عَاشُورَاءَ لِمَنْ غَفَلَ عَنْ إِنْشَاءِ الصَّوْمِ لَهُ

ibnhibban:3619 – ʿUmar b. Muḥammad al-Hamdānī > al-Dawraqī > Abū ʿĀṣim > Yazīd b. Abū ʿUbayd > Salamah b. al-Akwaʿ

[Machine] The Messenger of Allah ﷺ sent a man who had embraced Islam to make an announcement among the people, saying, "Today is the day of Ashura. Whoever had eaten should not eat anything else for the remainder of the day, and whoever had not eaten or drunk anything should observe fasting."  

ابن حبّان:٣٦١٩ – أَخْبَرَنَا عُمَرُ بْنُ مُحَمَّدٍ الْهَمْدَانِيُّ حَدَّثَنَا الدَّوْرَقِيُّ حَدَّثَنَا أَبُو عَاصِمٍ عَنْ يَزِيدَ بْنِ أَبِي عُبَيْدٍ عَنْ سَلَمَةَ بْنِ الْأَكْوَعِ

أَنَّ رَسُولَ اللَّهِ ﷺ بَعَثَ رَجُلًا مِنْ أَسْلَمَ يُؤَذِّنُ فِي النَّاسِ «أَنَّ الْيَوْمَ يَوْمُ عَاشُورَاءَ فَمَنْ أَكَلَ فَلَا يَأْكُلْ شَيْئًا بَقِيَّةَ يَوْمِهِ وَمَنْ لَمْ يَكُنْ أَكَلَ أَوْ شَرِبَ فَلْيَصُمْ»