Once the Prophet ﷺ ordered a person on 'Ashura' (the tenth of Muharram) to announce, "Whoever has eaten, should not eat any more, but fast, and who has not eaten should not eat, but complete his fast (till the end of the day).
أَنَّ النَّبِيَّ ﷺ بَعَثَ رَجُلاً يُنَادِي فِي النَّاسِ يَوْمَ عَاشُورَاءَ أَنْ مَنْ أَكَلَ فَلْيُتِمَّ أَوْ فَلْيَصُمْ وَمَنْ لَمْ يَأْكُلْ فَلاَ يَأْكُلْ
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.' "
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
[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."
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»