Sahih al-bukhari:4503 What has been said about Fãtihat al-Kitab (i.e., the Opening of the Book) Book 65, Hadith 30

Narrated `Abdullah: That Al-Ash’ath entered upon him while he was eating. Al-Ash’ath said, “Today is ‘Ashura.” I said (to
him), “Fasting had been observed (on such a day) before (the order of compulsory fasting in)
Ramadan was revealed. But when (the order of fasting in) Ramadan was revealed, fasting (on
‘Ashura’) was given up, so come and eat.”