Sahih Muslim Book 27, Hadith 16
We came to Allah's Messenger (ﷺ) requesting him to provide us with riding camels. He (the Holy Prophet) said: There is nothing with me with which I should equip you. By Allah, I would not provide you with (riding camels). Then Allah's Messenger (ﷺ) sent to us three camels with spotted bumps. We said: We came to Allah's Messenger (ﷺ) asking him to equip us with riding animals. He took an oath that he could not equip us. We came to him and informed him. He said: By Allah, I do not take an oath, but when I find the other thing better than that, I do that which is better.
I visited Abu Musa and lie was eating fowl's meat. The rest of the hadith is the same with this addition that he (the Holy Prophet) said: By Allah, I did not forget it.
We walked on foot and came to Allah's Apostle (may peace he upon him) asking him to provide us with mounts. The rest of the hadith is the same.