كتاب الصيام
13
The Book of Fasting
(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
(15)
باب جواز الصوم والفطر في شهر رمضان للمسافر في غير معصية إذا كان سفره مرحلتين فأكثر وأن الأفضل لمن أطاقه بلا ضرر أن يصوم ولمن يشق عليه أن يفطر
Sahih Muslim 1115 b

'Amr b. al-Hasan is reported to have said that he heard Jabir b. 'Abdullah (Allah be pleased with both of them) as saying that the Messenger of Allah (ﷺ) saw a man. The rest of the hadith is the same as mentioned above.

حَدَّثَنَا عُبَيْدُ اللَّهِ بْنُ مُعَاذٍ، حَدَّثَنَا أَبِي، حَدَّثَنَا شُعْبَةُ، عَنْ مُحَمَّدِ بْنِ عَبْدِ الرَّحْمَنِ، قَالَ سَمِعْتُ مُحَمَّدَ بْنَ عَمْرِو بْنِ الْحَسَنِ، يُحَدِّثُ أَنَّهُ سَمِعَ جَابِرَ بْنَ عَبْدِ اللَّهِ، - رضى الله عنهما - يَقُولُ رَأَى رَسُولُ اللَّهِ صلى الله عليه وسلم رَجُلاً بِمِثْلِهِ ‏.‏
Reference : Sahih Muslim 1115 b
In-book reference : Book 13, Hadith 119
USC-MSA web (English) reference : Book 6, Hadith 2475
  (deprecated numbering scheme)