بُلُوغُ الْمَرَامِ
Bulugh al-Maram 159
The Book of Prayer
وَعَنْ أَبِي هُرَيْرَةَ - رضى الله عنه - قَالَ: قَالَ رَسُولُ اَللَّهِ - صلى الله عليه وسلم -{ إِذَا اِشْتَدَّ اَلْحَرُّ فَأَبْرِدُوا بِالصَّلَاةِ, فَإِنَّ شِدَّةَ اَلْحَرِّ مِنْ فَيْحِ جَهَنَّمَ } مُتَّفَقٌ عَلَيْهِ [1] .
Narrated Abu Hurairah (RA): Allah's Messenger (ﷺ) said: "When it is hot, delay the (Zuhr) prayer till it cools down, for the intensity of heat is from the exhalation of Hell." [Agreed upon].
Sunnah.com reference: Book 2, Hadith 9