Musnad Ahmad 30:1984

Husayn narrated to us, he said: Ibn Abi Dhi'b narrated to us, from Abu al-Walid and 'Abd al-Rahman ibn Sa'd, from Abu Hurayrah, from the Prophet, peace and blessings of Allah be upon him, who said: "Indeed, the intensity of the heat is from the scorching breath of Hell, so cool down with the prayer."