Sahih Bukhari

Narrated Tawus:Ibn `Abbas said, ""Allah's Messenger (ﷺ) travelled in the month of Ramadan and he fasted till he reached (a place called) 'Usfan, then he asked for a tumbler of water and drank it by the daytime so that the people might see him. He broke his fast till he reached Mecca."" Ibn `Abbas used to say, ""Allah's Apostle fasted and sometimes did not fast while traveling, so one may fast or may not (on journeys)