Sahih al-Bukhari 6110

It is related that Zahdam al-Jarmi said, "We were with Abu Musa al-Ash'ari, as there was friendship and mutual favours between us and the tribe of Jarm. He was brought some food which contained chicken meat. Among those present was a man from the Banu Taym who was reddish as if he were one of the Greek clients. He did not approach the food and Abu Musa said to him, 'Come over. I have seen the Messenger of Allah, may Allah bless him and grant him peace, eating this.' He said, 'I saw them eating something filthy and I swore that I would never eat that.' Abu Musa said, 'Come over and I will inform you about that. We went to the Messenger of Allah, may Allah bless him and grant him peace, in the group of the Ash'arites, asking him to give us mounts. He was dividing up some of the livestock of the zakat. (Ayyub said, 'I think that he said that the Prophet, may Allah bless him and grant him peace, was angry.') He said, 'By Allah, I will not give you mounts, and I do not have any mounts to give you.' We left and then the Messenger of Allah, may Allah bless him and grant him peace, was brought some camels as booty. He said, 'Where are those Ash'arites?' He commanded for us five camels with white humps. When we left, I said to my companions, 'We went to the Prophet, may Allah bless him and grant him peace, to ask for mounts and He swore that he would not give us any mounts and then he sent for us gave us mounts. The Messenger of Allah. may Allah bless him and grant him peace, has forgotten his oath. By Allah, if we are take advantage of the Messenger of Allah, may Allah bless him and grant him peace, forgetting his oath, we will never prosper! Let us go back to the Messenger of Allah, may Allah bless him and grant him peace, and remind him of his oath.' So we returned to him and said, 'Messenger of Allah, we came to you and asked you to give us mounts and you swore that you would not give us mounts and then you gave us mounts. We thought (or 'we realised') that you had forgotten your oath.' He said, 'Go, Allah gave you mounts. By Allah, Allah willing, I will never make an oath and then see something better than it without doing the thing that is better and then doing expiation for it.'" Hammad ibn Zayd corroborated it from Ayyub from Abu Qilaba and al-Qasim ibn 'Asim al-Kalbi. Another isnad of this from Zahdam. Another isnad from Zahdam.