Sahih Muslim Book - 13, Hadith - 2668

حَدَّثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ حَدَّثَنَا حَاتِمٌ - يَعْنِى ابْنَ إِسْمَاعِيلَ - عَنْ يَزِيدَ بْنِ أَبِى عُبَيْدٍ عَنْ سَلَمَةَ بْنِ الأَكْوَعِ - رضى الله عنه - أَنَّهُ قَالَ بَعَثَ رَسُولُ اللَّهِ -صلى الله عليه وسلم- رَجُلاً مِنْ أَسْلَمَ يَوْمَ عَاشُورَاءَ فَأَمَرَهُ أَنْ يُؤَذِّنَ فِى النَّاسِ « مَنْ كَانَ لَمْ يَصُمْ فَلْيَصُمْ وَمَنْ كَانَ أَكَلَ فَلْيُتِمَّ صِيَامَهُ إِلَى اللَّيْلِ ».

It was narrated that Salamah bin Al-Akwa said: “The Messenger of Allah sent a man from Aslam on the day of Ashura and told him to announce to the people: ‘Whoever is not fasting, let him fast, and whoever has eaten, let him complete his fast until nightfall.’”