Sahih Muslim 1113
Sahih Muslim · Book 13: The Book of Fasting · 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
Ibn Abbas (Allah be pleased with him) reported:
وَحَدَّثَنَا أَبُو كُرَيْبٍ ، حَدَّثَنَا وَكِيعٌ ، عَنْ سُفْيَانَ ، عَنْ عَبْدِ الْكَرِيمِ ، عَنْ طَاوُسٍ ، عَنِ ابْنِ، عَبَّاسٍ - رضى الله عنهما - قَالَ لاَ تَعِبْ عَلَى مَنْ صَامَ وَلاَ عَلَى مَنْ أَفْطَرَ قَدْ صَامَ رَسُولُ اللَّهِ صلى الله عليه وسلم فِي السَّفَرِ وَأَفْطَرَ .
Do not condemn one who observes fast, or one who does not observe (in a journey). for the Messenger of Allah (ﷺ) observed fast in a journey or he did not observe it (too).