I was with Ibn Umar when a man asked him, "I vowed to fast every Tuesday or Wednesday for as long as I live, but this day has fallen on the Day of Sacrifice."Ibn Umar replied, "Allah has commanded the fulfillment of vows, and we have been forbidden to fast on the Day of Sacrifice."The man repeated his question, and Ibn Umar gave him the same answer, adding nothing further.In another narration, "The Messenger of Allah ﷺ forbade fasting on this day."And in yet another narration, he added, "He said, 'Indeed, in the Messenger of Allah you have an excellent example' [Ahzab 33:21]. He did not fast on the day of Adha or the day of Fitr, nor did he consider it permissible to fast on them."
كنت مع ابن عمر، فسأله رجل، فقال: نذرت أن أصوم كل يوم ثلاثاء أو أربعاء ما عشت، فوافقت هذا اليوم يوم النحر، فقال: أمر الله بوفاء النذر، ونهينا أن نصوم يوم النحر، فأعاد عليه، فقال مثله لا يزيد عليه. وفي رواية: ونهى رسول الله ﷺ عن صوم هذا اليوم وزاد في رواية: فقال: {لقد كان لكم في رسول الله أسوة حسنة} [سورة الأحزاب: ٢١] لم يكن يصوم يوم الأضحى والفطر، ولا يرى صيامهما.
Bukhari narrated it in the book of Oaths and Vows (6706), via Yunus, and Muslim narrated it in the book of Fasting (1139), via Ibn Awn, both of them from Ziyad bin Jubayr, who related it. The wording given here is Bukhari's, and the other version is Muslim's. The additional wording belongs to Bukhari (6705), via Musa bin Uqba, who said that Hakeem bin Abu Hurra Aslami told him that he heard Abdullah bin Umar.Ibn Umar withheld from giving an answer because of the conflicting evidence he saw in the matter. The more apparent view is that one should not fast on those days, since a prohibition takes precedence over a mere permission. This is what is understood from Allah's saying, "Indeed, in the Messenger of Allah you have a good example" [Ahzab 33:21], meaning that he did not fast on the days of Eid al-Fitr and Eid al-Adha. Is one obligated to make up for it afterward? The more apparent view among the Shafiis is that no make-up is required, while others hold that making it up is obligatory.