The people of the pre-Islamic era had two days each year on which they would celebrate and play. When the Prophet ﷺ came to Medina, he said, "You had two days on which you used to play, but Allah has replaced them for you with two better days, the day of Fitr and the day of Adha."
أخبرنا علي بن حجر قال أنبأنا إسمعيل قال حدثنا حميد
كان لأهل الجاهلية يومان في كل سنة يلعبون فيهما فلما قدم النبي ﷺ المدينة قال كان لكم يومان تلعبون فيهما وقد أبدلكم الله بهما خيرا منهما يوم الفطر ويوم الأضحى
[Its chain of transmission is sahih] Abu Dawud narrated it in Kitab al-Salah, Bab Salat al-Idayn, no. 1134, from the hadith of Humayd Tawil with this same wording, and he explicitly stated that he heard it directly, as recorded by Ahmad, 3/250, and it is also found in al-Kubra, no. 1755. Hakim graded it sahih according to the criteria of Muslim, 1/294, and Dhahabi agreed with him.