The Messenger of Allah ﷺ forbade fasting on two days, the day of Fitr and the day of Adha.
نهي رسول الله ﷺ عن صومين: يوم الفطر، ويوم الأضحى.
Muslim narrated it in the Book of Fasting (1140), from Ibn Numayr (that is, Muhammad bin Abdullah bin Numayr), who said, my father narrated to us, Saad bin Saeed (al-Ansari) narrated to us, Amrah informed me, from Ayesha, and he mentioned it.