Yahya related to me from Malik from Zayd ibn Aslam from Ata ibnYasar that the Messenger of Allah, may Allah bless him and grant himpeace, said, "Scorching heat is a part of the blast of Jahannam. So,when the heat is fierce, delay the prayer until it gets cooler."He added in explanation, "The Fire complained to its Lord andsaid, 'My Lord, part of me has eaten another part,' so He allowed ittwo breaths in every year, a breath in winter and a breath in summer."
Arabic/English book reference: Book 1, Hadith 27