Musnad Abu Ya'la al-Mawsili 155:31

'Amr al-Naqid narrated to us, Sufyan ibn 'Uyaynah narrated to us, from al-Zuhri, from Sa'id ibn al-Musayyib, from Abu Hurayrah, who said: The Messenger of Allah (ﷺ) said: "When the heat intensifies, then delay the prayer until it cools down, for the intensity of the heat is from the scorching breath of Hell. The Fire complained to its Lord and said: 'O Lord, parts of me are consuming other parts.' So He permitted it two breaths: one breath in the winter and one breath in the summer. That is the most intense heat you find and the most intense cold (zamharir) you find."