Fasting

Bukhari :: Book 3 :: Volume 31 :: Hadith 147

Narrated Salama bin Al-Akwa:

Once the Prophet 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).