"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."'
Sunan an-Nasa'i Book 22, Hadith 232
← Previous Hadith "The Messenger of Allah said on the day of Ashura: Is there anyone among you who has eaten today?' They said: Some of us are fasting and some of us are not.' He said: 'Do not eat for the rest of the day, and send word to the people of Al-Al-Arud telling them not to eat for the rest of the day."'

Sunan an-Nasa'i Book 22, Hadith 231 Next Hadith → "The Messenger of Allah came to me one day and said: 'Do you have anything (to eat)?' I said: 'No.' he said: 'Then I am fasting.' Then he came to me after that day, and I had been given some Hais. I had kept some for him as he liked Hais. She said: 'O Messenger of Allah, we have been given some Hais and I kept some for you.' He said: 'Bring it here. I started the day fasting.' Then he ate some of it, then he said: 'The likeness of a voluntary fast is that of a man who allocated some of his wealth to give in charity; if he wishes he may go ahead and give it, and if he wishes he may keep it."'

Sunan an-Nasa'i Book 22, Hadith 233