'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.
Sahih Muslim Book 13, Hadith 182
← Previous Hadith I had taken a vow that I would fast on the day (but it accidentally) synchronises with the day of Adha or the day of Fitr. Thereupon Ibn 'Umar (Allah be pleased with him) said: Allah, the Exalted, has commanded fulfilling of the vow, but the Messenger of Allah (ﷺ) has forbidden the observance of fast on this day.

Sahih Muslim Book 13, Hadith 181 Next Hadith → The days of Tashriq are the days of eating and drinking.

Sahih Muslim Book 13, Hadith 183