We were with Abu Musa Ashari, and between us and this clan of Jarm there was a bond of brotherhood. Food was brought containing chicken meat, and among the people sat a red-complexioned man who did not come near the food.Abu Musa said, "Come close, for I saw the Messenger of Allah ﷺ eating it."The man replied, "I saw it eating something I found disgusting, so I swore never to eat it."Abu Musa said, "Come close, let me tell you something. I came to the Prophet ﷺ with a group of Asharis and found him angry, distributing camels from the camels of charity. We asked him to give us mounts, but he swore he would not provide us with any. He said, 'I have nothing to mount you on.'Then some captured camels were brought to the Messenger of Allah ﷺ, and he asked, 'Where are the Asharis? Where are the Asharis?' He gave us five fine, white-humped camels.We did not stay long before I said to my companions, 'The Messenger of Allah ﷺ has forgotten his oath. By Allah, if we let the Messenger of Allah ﷺ overlook his oath, we shall never prosper.'So we returned to the Prophet ﷺ and said, 'Messenger of Allah, we asked you for mounts and you swore you would not provide us any. We think you have forgotten your oath.'He said, 'It is Allah who provided you with mounts. By Allah, if Allah wills, I never swear an oath and then see something better than it without doing what is better and absolving myself of the oath.'"
كنا عند أبي موسى الأشعري- وكان بيننا وبين هذا الحي من جرم إخاء- فأتي بطعام فيه لحم دجاج، وفي القوم رجل جالس أحمر فلم يدن من طعامه، قال: ادن فقد رأيت رسول الله ﷺ يأكل منه، قال: إني رأيته يأكل شيئا فقذرته، فحلفت أن لا أكله، فقال: ادن أخبرك أو أحدثك إني أتيت النبي ﷺ في نفر من الأشعريين، فوافقته وهو غضبان، وهو يقسم نعما من نعم الصدقة، فاستحملناه فحلف أن لا يحملنا، قال: ما عندي ما أحملكم عليه، ثم أتي رسول الله ﷺ بنهب من إبل، فقال: أين الأشعريون؟ أين الأشعريون؟ قال: فأعطانا خمس ذود غر الذرى، فلبثنا غير بعيد، فقلت لأصحأبي: نسي رسول الله ﷺ يمينه، فوالله لئن تغفلنا رسول الله ﷺ يمينه لا تفلح أبدا، فرجعنا إلى النبي ﷺ فقلنا: يا رسول الله إنا استحملناك، فحلفت أن لا تحملنا، فظننا أنك نسيت يمينك، فقال: إن الله هو حملكم، إني والله-. إن شاء الله- لا أحلف على يمين، فأرى غيرها خيرا منها إلا أتيت الذي هو خير، وتحللتها.
Bukhari narrated it in the Book of Sacrifices and Hunting (5518), and Muslim in the Book of Oaths (1649:9), both of them from the hadith of Ayub, from Qasim (he is Ibn Aasim), from Zahdam Jarmi, who mentioned it. The wording given here is Bukhari's.