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.
أَنْ أَصُومَ يَوْمًا فَوَافَقَ يَوْمَ أَضْحَى أَوْ فِطْرٍ فَقَالَ ابْنُ عُمَرَ ؓ أَمَرَ اللَّهُ تَعَالَى بِوَفَاءِ النَّذْرِ وَنَهَى رَسُولُ اللَّهِ ﷺ عَنْ صَوْمِ هَذَا الْيَوْمِ
[Machine] Is it obligatory to fast every Wednesday, and if I happened to fast on the day of Eid al-Adha or Eid al-Fitr, would that be acceptable? Ibn Umar replied, "Allah has commanded us to fulfill our vows, and the Messenger of Allah ﷺ has prohibited us from fasting on the day of sacrifice."
أَنْ يَصُومَ كُلَّ يَوْمِ أَرْبِعَاءَ فَأَتَى ذَلِكَ عَلَيَّ يَوْمِ أَضْحًى أَوْ فِطْرٍ؟ فَقَالَ ابْنُ عُمَرَ أَمَرَ اللهُ بِوَفَاءِ النَّذْرِ وَنَهَانَا رَسُولُ اللهِ ﷺ عَنْ صَوْمِ يَوْمِ النَّحْرِ
[Machine] "To fast for a day that coincides with the day of Eid al-Adha or Eid al-Fitr, Ibn Umar said that Allah commanded the fulfillment of vows and the Messenger of Allah ﷺ forbade us from fasting on this day."
أَنْ يَصُومَ يَوْمًا فَوَافَقَ يَوْمَئِذٍ عِيدَ أَضْحَى أَوْ يَوْمَ فِطْرٍ فَقَالَ ابْنُ عُمَرَ أَمَرَ اللهُ بِوَفَاءِالنَّذْرِ وَنَهَانَا رَسُولُ اللهِ ﷺ عَنْ صَوْمِ هَذَا الْيَوْمِ