Sahih al-Bukhari 5518

It is related that Zahdam said, "We were with Abu Musa al-Ash'ari, and there was friendship between us and this tribe of Jarm. He was brought some food which contains chicken meat. There was a man with a red complexion sitting there who did not go near the food. Abu Musa said, 'Come near! I saw the Prophet, may Allah bless him and grant him peace, eat it.' He replied, 'I saw it eat something filthy and I have taken an oath not to eat it.' He said, 'Come and I will inform – or tell – you about that. I came to the Prophet, may Allah bless him and grant him peace, among the group of the Ash'arites, which happened to be at a time when he was angry. He was dividing up some of the zakat camels. We asked him to give us mounts and he swore that he would not give us mounts. He said, 'I have nothing to let you ride.' Then the Prophet, may Allah bless him and grant him peace, was brought some camels as booty and asked, 'Where are the Ash'arites? Where are the Ash'arites?' He gave us five camels with white humps. We went a short distance and I said to my companions, 'The Messenger of Allah, may Allah bless him and grant him peace, forgot his oath. By Allah, if we take advantage of the Prophet, may Allah bless him and grant him peace, forgetting his oath, we will never be successful!' So we went back to the Prophet, may Allah bless him and grant him peace, and said, 'Messenger of Allah, you gave us mounts when you swore that you would not give us mounts. We think that you have forgotten your oath.' He answered, 'It is Allah who has given you mounts. By Allah, if Allah wills, 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.'"