Musnad Ahmad 32:1526

Muhammad ibn Abdullah narrated to us, Humayd narrated to us, from Anas ibn Malik, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "I arrived in Medina, and the people of Medina had two days in which they used to play during the Jahiliyyah." He said: "I arrived among you, and you had two days in which you used to play. Verily, Allah the Almighty has replaced them for you with two days better than them: the day of al-Fitr and the day of al-Nahr."