Observing Saum on the first day of 'Eid-ul-Adha. Sahih al-Bukhari 1994
Arabic hadith text
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 عُمَرَأَمَرَ اللَّهُ بِوَفَاءِ النَّذْرِ، وَنَهَى النَّبِيُّ صلى الله عليه وسلم عَنْ صَوْمِ هَذَا الْيَوْمِ.
Translation
Narrated Ziyad bin Jubair
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).