Mu'jam Kabir Tabarani 15122 — We went in to Sayyiduna A'idh bin Amr

Abdullah bin Abi Sa'd narrates: We went in to Sayyiduna A'idh bin Amr (may Allah be pleased with him) on the day of Ashura, and he said: O boy, milk (an animal) for them. The boy went to a milch she-camel, milked her, and then brought the milk to them. He said to the man on his right: Drink. He said: I am fasting. He said: May Allah accept from you and from us. Then he said (the same) to the second, and he too said: I am fasting, so he said the same as before. Then he said (the same) to the third, and he said likewise. Then he said: Are all of you fasting? Soon you will give this day the status of Ramadan. We used to fast this day only when Ramadan had not been made obligatory upon us; then when Ramadan was made obligatory upon us, the fast of Ramadan abrogated the fast of this day. This day is a day of voluntary fasting, not obligatory; so whoever wishes may fast, and whoever wishes may not fast. When the people heard this, they all broke their fast. (These are the words of the narration of Zayd bin al-Harish.)