Ibn ‘Abbas said that it was the custom of God’s messenger not to eat on the middle days* of the month whether travelling or not.
*Literally, the days of the white (nights). These are the days following the thirteenth, fourteenth, and fifteenth nights of the month, the nights when there is most moonlight.
Narrated Hafsa said there were four things the Prophet never omitted:
fasting on ‘Ashura’, the first ten days of Dhul Hijja* and three days every month, and praying two rak'as before dawn.
*The Arabic has simply 'the ten', to be understood as translated above.
Jabir b. Samura said, “God’s messenger used to command us to observe the day of ‘Ashura’ as a fast, urge us to observe it and pay attention to us when it came; but when Ramadan was made obligatory he neither commanded nor forbade us to observe it, nor did he pay attention to us when it came.”
