كتاب الْمَسَاجِدِ وَمَوَاضِعِ الصَّلاَةِ
5  
The Book of Mosques and Places of Prayer
(32)
Chapter: The recommendation to delay Zuhr (until it has cooled down) in severe heat for one who finds it too hot in route to join the congregation
(32)
باب اسْتِحْبَابِ الإِبْرَادِ بِالظُّهْرِ فِي شِدَّةِ الْحَرِّ لِمَنْ يَمْضِي إِلَى جَمَاعَةٍ وَيَنَالُهُ الْحَرُّ فِي طَرِيقِهِ
Sahih Muslim 615 e

Hammam b. Munabbih reported:

This is what Abu Huraira narrated to us from the Prophet and he transmitted some ahadith-one of them was that the Messenger of Allah (ﷺ) said: Let the heat become less severe before prayer, for the intensity of heat is from the exhalation of Hell.
حَدَّثَنَا ابْنُ رَافِعٍ، حَدَّثَنَا عَبْدُ الرَّزَّاقِ، حَدَّثَنَا مَعْمَرٌ، عَنْ هَمَّامِ بْنِ مُنَبِّهٍ، قَالَ هَذَا مَا حَدَّثَنَا أَبُو هُرَيْرَةَ، عَنْ رَسُولِ اللَّهِ صلى الله عليه وسلم فَذَكَرَ أَحَادِيثَ مِنْهَا وَقَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏ "‏ أَبْرِدُوا عَنِ الْحَرِّ فِي الصَّلاَةِ فَإِنَّ شِدَّةَ الْحَرِّ مِنْ فَيْحِ جَهَنَّمَ ‏"‏ ‏.‏
Reference : Sahih Muslim 615e
In-book reference : Book 5, Hadith 233
USC-MSA web (English) reference : Book 4, Hadith 1288
  (deprecated numbering scheme)