Musnad Ahmad 788:138

Ibn Abi ‘Adi narrated to us, from Sulayman—meaning al-Taymi—from Abu al-Sulayl, from Zahdam, from Abu Musa, who said: We went to the Prophet, peace and blessings of Allah be upon him, seeking mounts from him, and he said: "By Allah, I will not provide you with mounts." So we returned, but then he sent to us three camels with humps. Some of us said to others: "The Prophet, peace and blessings of Allah be upon him, swore that he would not provide us with mounts." So we came to him and said: "You swore that you would not provide us with mounts." He said: "It was not I who provided you with mounts; rather, it was Allah the Exalted who provided you with mounts. There is no oath that I swear, then see something else as better than it, except that I come to that which is better."