Abu Salamah (may Allah have mercy on him) narrates from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that he (peace and blessings be upon him) said: "When the heat is severe, cool off the prayer (that is, delay it) (they transmitted the words 'an al-salah, whereas Ibn Mawhab transmitted the words bi al-salah), for the intensity of the heat comes from the breath of Hell."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2057