(32) باب اسْتِحْبَابِ الإِبْرَادِ بِالظُّهْرِ فِي شِدَّةِ الْحَرِّ لِمَنْ يَمْضِي إِلَى جَمَاعَةٍ وَيَنَالُهُ الْحَرُّ فِي طَرِيقِهِ
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.
Reference: Sahih Muslim 616
In-book reference: Book 5, Hadith 236
USC-MSA web (English) reference(deprecated numbering scheme): Book 4, Hadith 1289