بُلُوغُ الْمَرَامِ
Bulugh al-Maram 499
The Book of Prayer
وَعَنْ أَنَسٍ قَالَ: { قَدِمَ رَسُولُ اَللَّهِ - صلى الله عليه وسلم -اَلْمَدِينَةَ, وَلَهُمْ يَوْمَانِ يَلْعَبُونَ فِيهِمَا. فَقَالَ: "قَدْ أَبْدَلَكُمُ اَللَّهُ بِهِمَا خَيْرًا مِنْهُمَا: يَوْمَ اَلْأَضْحَى, وَيَوْمَ اَلْفِطْرِ } أَخْرَجَهُ أَبُو دَاوُدَ, وَالنَّسَائِيُّ بِإِسْنَادٍ صَحِيحٍ [1] .
Narrated Anas (RA) that when Allah's Messenger (ﷺ) came to al-Madinah, the people had two days on which they engaged in games. He (ﷺ) said: "Allah has substituted for you something better than them: the day of sacrifice and the day of breaking the fast." [Reported by Abu Dawud and an-Nasa'i; with a Sahih Isnad (authentic chain)].
Sunnah.com reference: Book 2, Hadith 427