Musnad Ahmad 30:711

Muhammad ibn Bakr narrated to us, Ibn Jurayj narrated to us, Ibn Shihab informed me, from Sa'id ibn al-Musayyib and Abu Salamah ibn 'Abd al-Rahman, from Abu Hurayrah, from the Prophet, peace and blessings of Allah be upon him, who said: "When the heat becomes intense, then delay the prayer until it cools down, for the intensity of the heat is from the scorching breath of Hell."