صحيح البخاري Sahih Bukhari كتاب الصوم The Book of As-Saum (The Fasting).
بَابُ قَوْلِ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ لِمَنْ ظُلِّلَ عَلَيْهِ، وَاشْتَدَّ الْحَرُّ: «لَيْسَ مِنَ الْبِرِّ الصَّوْمُ فِي السَّفَرِ»:

(36) Chapter. The saying of the Prophet ﷺ to the person observing Saum (fast) who was being shaded on a very hot day, "It is not from Al-Birr (righteousness) to observe As-Saum (the fast) on a journey."

1 hadith
Hadith 1946
حَدَّثَنَا آدَمُ ، حَدَّثَنَا شُعْبَةُ ، حَدَّثَنَا مُحَمَّدُ بْنُ عَبْدِ الرَّحْمَنِ الْأَنْصَارِيُّ ، قَالَ : سَمِعْتُ مُحَمَّدَ بْنَ عَمْرِو بْنِ الْحَسَنِ بْنِ عَلِيٍّ ، عَنْ جَابِرِ بْنِ عَبْدِ اللَّهِ رَضِيَ اللَّهُ عَنْهُمْ ، قَالَ : " كَانَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ فِي سَفَرٍ ، فَرَأَى زِحَامًا وَرَجُلًا قَدْ ظُلِّلَ عَلَيْهِ ، فَقَالَ : مَا هَذَا ؟ فَقَالُوا : صَائِمٌ ، فَقَالَ : لَيْسَ مِنَ الْبِرِّ الصَّوْمُ فِي السَّفَرِ " .
Narrated Jabir bin `Abdullah: Allah's Apostle was on a journey and saw a crowd of people, and a man was being shaded (by them). He asked, "What is the matter?" They said, "He (the man) is fasting." The Prophet said, "It is not righteousness that you fast on a journey."
Hadith Reference Sahih Bukhari / The Book of As-Saum (The Fasting). / Hadith: 1946
Hadith Grading محدثین: أحاديث صحيح البخاريّ كلّها صحيحة