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 1116 c
Translation
Abu Sa'id al-Khudri (Allah be pleased with him) reported
We went out on an expedition with the Messenger of Allah (ﷺ) during Ramadan and neither the observer of the fast was found fault with for his fasting, nor the breaker of the fast for breaking it.