(22) باب النَّهْىِ عَنْ صَوْمِ، يَوْمِ الْفِطْرِ وَيَوْمِ الأَضْحَى
'A'isha (Allah be pleased with her) said that the Prophet (ﷺ) forbade to observe fast on two days-the day of Fitr and the day of Adha.
Reference: Sahih Muslim 1140
In-book reference: Book 13, Hadith 182
USC-MSA web (English) reference(deprecated numbering scheme): Book 6, Hadith 2538