Sunan an-Nasa'i, Book 42, Hadith 84 (In-Book) ⓘ

It was narrated from Zahdam that: Some chicken was brought to Abu Musa and a man moved away from the people. He said: "What is the matter with you?" He said: "I saw it eating something that I consider filthy, and I swore I would not eat it." Abu Musa said: "Come and eat, for I saw the Messenger of Allah eating it." And he told him to offer an expiation for his vow (Kafarat Al-Yamin)

أَخْبَرَنَا مُحَمَّدُ بْنُ مَنْصُورٍ، قَالَ حَدَّثَنَا سُفْيَانُ، قَالَ حَدَّثَنَا أَيُّوبُ، عَنْ أَبِي قِلاَبَةَ، عَنْ زَهْدَمٍ، أَنَّ أَبَا مُوسَى، أُتِيَ بِدَجَاجَةٍ فَتَنَحَّى رَجُلٌ مِنَ الْقَوْمِ فَقَالَ مَا شَأْنُكَ قَالَ إِنِّي رَأَيْتُهَا تَأْكُلُ شَيْئًا قَذِرْتُهُ فَحَلَفْتُ أَنْ لاَ آكُلَهُ ‏.‏ فَقَالَ أَبُو مُوسَى ادْنُ فَكُلْ فَإِنِّي رَأَيْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يَأْكُلُهُ ‏.‏ وَأَمَرَهُ أَنْ يُكَفِّرَ عَنْ يَمِينِهِ ‏.‏