Sahih Bukhari

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)