Prayer (Kitab Al-Salat): Details of Commencing Prayer
Dawud :: Book 3 : Hadith 1130
Narrated Anas ibn Malik:
When the Apostle of Allah (peace_be_upon_him) came to Medina, the people had two days on which they engaged in games. He asked: What are these two days (what is the significance)? They said: We used to engage ourselves on them in the pre-Islamic period. The Apostle of Allah (peace_be_upon_him) said: Allah has substituted for them something better than them, the day of sacrifice and the day of the breaking of the fast.