Sahih al-Bukhari 1994
Sahih al-Bukhari · Book 30: Fasting · Observing Saum on the first day of 'Eid-ul-Adha.
Narrated Ziyad bin Jubair:
حَدَّثَنَا مُحَمَّدُ بْنُ الْمُثَنَّى ، حَدَّثَنَا مُعَاذٌ ، أَخْبَرَنَا ابْنُ عَوْنٍ ، عَنْ زِيَادِ بْنِ جُبَيْرٍ ، قَالَ جَاءَ رَجُلٌ إِلَى ابْنِ عُمَرَ ـ رضى الله عنهما ـ فَقَالَ رَجُلٌ نَذَرَ أَنْ يَصُومَ يَوْمًا، قَالَ أَظُنُّهُ قَالَ الاِثْنَيْنِ، فَوَافَقَ يَوْمَ عِيدٍ. فَقَالَ ابْنُ عُمَرَ أَمَرَ اللَّهُ بِوَفَاءِ النَّذْرِ، وَنَهَى النَّبِيُّ صلى الله عليه وسلم عَنْ صَوْمِ هَذَا الْيَوْمِ.
A man went to Ibn `Umar I. 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).