It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "When it is hot, pray the prayer when it has cooled, for the intensity of the heat is due to the breath of Hell. And (also) Hell pleaded before its Lord, so Allah Almighty granted it permission to take two breaths every year, one breath in winter and the other in summer."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2058