The Book of Fasting
13/15. Chapter:
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
حَدَّثَنَا يَحْيَى بْنُ يَحْيَى، وَأَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ وَعَمْرٌو النَّاقِدُ وَإِسْحَاقُ بْنُ إِبْرَاهِيمَ عَنْ سُفْيَانَ، عَنِ الزُّهْرِيِّ، بِهَذَا الإِسْنَادِ . مِثْلَهُ . قَالَ يَحْيَى قَالَ سُفْيَانُ لاَ أَدْرِي مِنْ قَوْلِ مَنْ هُوَ يَعْنِي وَكَانَ يُؤْخَذُ بِالآخِرِ مِنْ قَوْلِ رَسُولِ اللَّهِ صلى الله عليه وسلم .
This hadith is narrated on the authority of Zuhri with the same chain of transmitters. Yahya (one of the narrators) said that Sufyan (the narrator) had stated: I do not know whose statement it is:" It is the last word of the Messenger of Allah (ﷺ) which is accepted as (final as it abrogates the previous ones)."
Reference : Sahih Muslim 1113bIn-book reference : Book 13, Hadith 111USC-MSA web (English) reference : Book 6, Hadith 2467