Sahih al-Bukhari 6108

Abu Burda ibn Abi Musa related that Abu Musa al-Ash'ari said, "I went to the Prophet, may Allah bless him and grant him peace, with a group of Ash'arites to ask him to give us mounts. He said, 'By Allah, I will not give you mounts and I do not have anything which you can ride,' Then we stayed there as long as Allah wished us to stay and then three camels with white humps were brought to him and he had us ride them. When we left, we – or some of us – said, 'By Allah, we will have no blessing! We went to the Prophet, may Allah bless him and grant him peace, to ask him for mounts and he swore that he would not give us mounts and then he gave us mounts.'" Abu Musa said, "We went to the Prophet, may Allah bless him and grant him peace, and mentioned that to him and he said, 'I did not give you mounts. Allah gave you mounts. By Allah, Allah willing, I will never swear an oath and then see something better than it but that I will do that which is better and expiate my oath." Hammad said, "But that I will expiate my oath and do that which is better," or "I will do that which is better and expiate my oath."