Musnad Ahmad 32:1678

'Affan narrated to us, Hammad narrated to us, Humayd informed us, he said: I heard Anas ibn Malik say: The Messenger of Allah (may Allah bless him and grant him peace) arrived in Medina, and they had two days in which they would play. The Messenger of Allah (may Allah bless him and grant him peace) said: "What are these two days?" They said: "We used to play in them during the Pre-Islamic Period (Jahiliyyah)." He said: "Indeed, Allah has replaced them for you with two that are better than them: the day of Al-Fitr and the day of Al-Nahr."