Sahih Muslim 615
Sahih Muslim · Book 5: The Book of Mosques and Places of Prayer · 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
Hammam b. Munabbih reported:
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 " .
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.