(22) باب النَّهْىِ عَنْ صَوْمِ، يَوْمِ الْفِطْرِ وَيَوْمِ الأَضْحَى
Abu Huraira (Allah be pleased with him) reported that the Messenger of Allah (ﷺ) forbade fasting on these two days. 'Id-ul-Adha and 'Id-ul-Fitr.
Reference: Sahih Muslim 1138
In-book reference: Book 13, Hadith 178
USC-MSA web (English) reference(deprecated numbering scheme): Book 6, Hadith 2534