Musnad Ahmad 30:495

'Abd al-Razzaq narrated to us, Ma'mar and Ibn Jurayj narrated to us, from al-Zuhri, from Ibn al-Musayyib and Abu Salamah, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) 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."