Musnad Abu Ya'la al-Mawsili 129:103

On the authority of Anas, may Allah be pleased with him, that the Ansar had two days in the pre-Islamic period during which they would play. When the Messenger of Allah, peace and blessings of Allah be upon him, arrived, he said: "Allah has replaced them for you with two days better than them: al-Fitr and al-Adha."