Hamzat al-Aslami asked the Prophet (ﷺ): Messenger of Allah, I am a man who keeps perpetual fast, may I fast while on a journey? He replied: Fast if you like, or break your fast if you like.
Sunan Abi Dawud Book 14, Hadith 90
← Previous Hadith If a man falls ill during Ramadan and he dies, while he could not keep the fast, food will be provided (for the poor men) on his behalf ; there is no atonement (for his fasts) due from him. If there is some vow which he could not fulfill, his heir must atone on his behalf.

Sunan Abi Dawud Book 14, Hadith 89 Next Hadith → I said: Messenger of Allah. I am a master of mounts and I use them ! I myself travel on them and I rent them. This month, that is, Ramadan, happend to come to me (while I am on a journey), and I find myself strong enough (to fast) as I am young, and I find that it is easier for me to fast than to postpone it, and i becomes debt due from me. Does it bring me more reward, Messenger of Allah, if I fast, or if I break ? He replied: Whichever you like, Hamzah.

Sunan Abi Dawud Book 14, Hadith 91