Sahih Muslim 1114
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
This hadith has been narrated by Ja'far with the same chain of transmitters and he added:
وَحَدَّثَنَاهُ قُتَيْبَةُ بْنُ سَعِيدٍ ، حَدَّثَنَا عَبْدُ الْعَزِيزِ، - يَعْنِي الدَّرَاوَرْدِيَّ - عَنْ جَعْفَرٍ ، بِهَذَا الإِسْنَادِ وَزَادَ فَقِيلَ لَهُ إِنَّ النَّاسَ قَدْ شَقَّ عَلَيْهِمُ الصِّيَامُ وَإِنَّمَا يَنْظُرُونَ فِيمَا فَعَلْتَ . فَدَعَا بِقَدَحٍ مِنْ مَاءٍ بَعْدَ الْعَصْرِ .
It was said to him (to the Holy Prophet): There are people to whom fasting has become unbearable and they are waiting how you do. He (the Holy Prophet) then called for a cup of water when it was afternoon. The rest of the hadith is the same.