It is permissible to fast or not to fast during Ramadan for one who is travelling for no sinful purpose, if his journey is two stages or further. But it is better for the one who is able to fast without suffering any harm to do so, and the one for whom it is difficult may break the fast Sahih Muslim 1113 e
Translation
Ibn 'Abbas (Allah be pleased with him) reported that the Messenger of Allah (ﷺ) journeyed during the month of Ramadan in a state of fasting till he reached 'Usfan. He then ordered a cup containing drinking water and he drank that openly so that the people might see it, and broke the fast (and did not resume it) till he reached Mecca. Ibn 'Abbas (Allah be pleased with him) said
Allah's Messenger (ﷺ) fasted and broke the fast, so he who wished fasted and he who wished to break it broke it.