It is narrated from Sayyiduna Abu Sa'id al-Khudri (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Pray Zuhr when it has cooled, for (indeed) the intensity of the heat is due to the breath of Hell."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2059