Sahih Bukhari
Sahih Bukhari Volume 001, Book 010, Hadith Number 513.
Hadith Section/Book: Sahih Bukhari Sahih Bukhari Book 10. Times of the Prayers
Narated By Abu Sa'id : That Allah's Apostle said, "Pray Zuhr prayer when it becomes (a bit) cooler as the severity of heat is from the raging of the Hell-fire."