(22) باب النَّهْىِ عَنْ صَوْمِ، يَوْمِ الْفِطْرِ وَيَوْمِ الأَضْحَى
Ziyad b. Jubair reported that a person came to Ibn 'Umar (Allah be pleased with them) and said:
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.
Reference: Sahih Muslim 1139
In-book reference: Book 13, Hadith 181
USC-MSA web (English) reference(deprecated numbering scheme): Book 6, Hadith 2537