Sahih al-Bukhari
Sahih al-Bukhari 2007
حَدَّثَنَا الْمَكِّيُّ بْنُ إِبْرَاهِيمَ، حَدَّثَنَا يَزِيدُ، عَنْ سَلَمَةَ بْنِ الأَكْوَعِ ـ رضى الله عنه ـ قَالَ أَمَرَ النَّبِيُّ صلى الله عليه وسلم رَجُلاً مِنْ أَسْلَمَ أَنْ أَذِّنْ فِي النَّاسِ " أَنَّ مَنْ كَانَ أَكَلَ فَلْيَصُمْ بَقِيَّةَ يَوْمِهِ، وَمَنْ لَمْ يَكُنْ أَكَلَ فَلْيَصُمْ، فَإِنَّ الْيَوْمَ يَوْمُ عَاشُورَاءَ ".
Al-Makkī ibn Ibrāhīm related to us: Yazīd related to us, from Salamah ibn al-Akwaʿ (may Allah be pleased with him), who said: The Prophet (Allah bless him and grant him peace) instructed a man from the tribe of Aslam to announce to the people: ‘Whoever has eaten, let him fast for the remainder of the day; and whoever has not eaten, let him fast—for today is the Day of ʿĀshūrāʾ.’
Translation notes
The Arabic specifically commands both those who have eaten and those who have not to fast that day; the former are to fast for the remainder of the day.