"Salamah told us that the Messenger of Allah said to a man: 'Announce the day of Ashura. Whoever has eaten let him not eat for the rest of the day, and whoever has not eaten, let him fast."' (Using translation from Nasāʾī 2321)  

أَنَّ رَسُولَ اللهِ ﷺ قَالَ لِرَجُلٍ «أَذِّنْ يَوْمَ عَاشُورَاءَ مَنْ أَكَلَ فَلْيُتِمَّ بَقِيَّةَ يَوْمِهِ وَمَنْ لَمْ يَكُنْ أَكَلَ فَلْيَصُمْ»