عَنْ هِنْدِ بْنِ أَسْمَاءَ رَضِيَ اللَّهُ عَنْهُ قَالَ: بَعَثَنِي رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَآلِهِ وَسَلَّمَ إِلَى قَوْمِي مِنْ أَسْلَمَ، فَقَالَ: ((مُرْ قَوْمَكَ فَلْيَصُومُوا هَذَا الْيَوْمَ وَيَوْمَ عَاشُورَاءَ، فَمَنْ وَجَدْتَّهُ مِنْهُمْ قَدْ أَكَلَ فِي أَوَّلِ يَوْمِهِ فَلْيَصُمْ آخِرَهُ))
It is narrated from Sayyiduna Hind bin Asma’ (may Allah be pleased with him), who says: The Messenger of Allah (peace and blessings be upon him) sent me to my tribe, Banu Aslam, and said: Command your people to fast on the day of ‘Ashura. If any of them has already eaten or drunk, then he should also fast for the remainder of the day.