وَحَدَّثَنَا يَحْيَى بْنُ يَحْيَى قَالَ قَرَأْتُ عَلَى مَالِكٍ عَنْ ابْنِ شِهَابٍ عَنْ أَبِي عُبَيْدٍ مَوْلَى ابْنِ أَزْهَرَ أَنَّهُ قَالَ: شَهِدْتُ الْعِيدَ مَعَ عُمَرَ بْنِ الْخَطَّابِ رَضِيَ اللَّهُ عَنْهُ فَجَاءَ فَصَلَّى ثُمَّ انْصَرَفَ فَخَطَبَ النَّاسَ فَقَالَ إِنَّ هَذَيْنِ يَوْمَانِ نَهَى رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ عَنْ صِيَامِهِمَا يَوْمُ فِطْرِكُمْ مِنْ صِيَامِكُمْ وَالْآخَرُ يَوْمٌ تَأْكُلُونَ فِيهِ مِنْ نُسُكِكُمْ

Ziyad b. Jubair reported that a person came to Ibn 'Umar (Allah be pleased with them) and said

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.