Musnad Ahmad 31:500

Muhammad ibn Ubayd narrated to us, he said: Al-A’mash narrated to us, from Abu Salih, from Abu Sa’id, he said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Delay the Dhuhr prayer until it cools down in the heat, for the intensity of the heat is from the exhalation of Hell." Thus Al-A’mash said: "From the exhalation of Hell."