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 616

Abu Dharr reported:

The Mu'adhdbin (the announcer of the hour of prayer) of the Messenger of Allah (ﷺ) called for the noon prayer. Upon this the Messenger of Allah (ﷺ) said: Let it cool down, let it cool down, or he said: Wait, wait for the intensity of heat is from the exhalation of Hell. When the heat is intense, delay the prayer till it becomes cooler. Abu Dharr said: (We waited) till we saw the shadow of the mounds.
حَدَّثَنِي مُحَمَّدُ بْنُ الْمُثَنَّى، حَدَّثَنَا مُحَمَّدُ بْنُ جَعْفَرٍ، حَدَّثَنَا شُعْبَةُ، قَالَ سَمِعْتُ مُهَاجِرًا أَبَا الْحَسَنِ، يُحَدِّثُ أَنَّهُ سَمِعَ زَيْدَ بْنَ وَهْبٍ، يُحَدِّثُ عَنْ أَبِي ذَرٍّ، قَالَ أَذَّنَ مُؤَذِّنُ رَسُولِ اللَّهِ صلى الله عليه وسلم بِالظُّهْرِ فَقَالَ النَّبِيُّ صلى الله عليه وسلم ‏"‏ أَبْرِدْ أَبْرِدْ ‏"‏ ‏.‏ أَوْ قَالَ ‏"‏ انْتَظِرِ انْتَظِرْ ‏"‏ ‏.‏ وَقَالَ ‏"‏ إِنَّ شِدَّةَ الْحَرِّ مِنْ فَيْحِ جَهَنَّمَ فَإِذَا اشْتَدَّ الْحَرُّ فَأَبْرِدُوا عَنِ الصَّلاَةِ ‏"‏ ‏.‏ قَالَ أَبُو ذَرٍّ حَتَّى رَأَيْنَا فَىْءَ التُّلُولِ ‏.‏
Reference : Sahih Muslim 616
In-book reference : Book 5, Hadith 234
USC-MSA web (English) reference : Book 4, Hadith 1289
  (deprecated numbering scheme)