From Sahih Bukhari (Hadith 1994):
Narrated Ziyad bin Jubair:A man went to Ibn `Umar and said, "A man vowed to fast one day (the sub-narrator thinks that he said that the day was Monday), and that day happened to be `Id day." Ibn `Umar said, "Allah orders vows to be fulfilled and the Prophet (ﷺ) forbade the fasting on this day (i.e. Id)
Reference: Bukhari 1994