Sahih Muslim Book 6, Hadith Number 2532.

Chapter : He who ate on the day of Ashura should abstain (from eating) for the rest of the day (as a mark of respect).

Khalid b. Dhakwan reported: I asked Rubayyi’ daughter of Mu’awwidh about fasting on the day of ‘Ashura. Thereupon she said: The Messenger of Allah (may peace he upon him) sent his messenger to the villages of the Ansar, and the rest of the Hadith is the same (but with this variation that one of the Companions) said: “We used to make toys out of wool and took (them to the mosque) along with us. When they (the children)asked us for food, we gave them these toys to play with, and these made them forgetful till they completed their fast.”