Musnad Ahmad 626:52

Ishaq ibn Yusuf al-Azraq narrated to us, from Sharik, from Bayan ibn Bishr, from Qays ibn Abi Hazim, from al-Mughirah ibn Shu’bah, who said: We used to pray the Dhuhr prayer with the Prophet of Allah, peace and blessings of Allah be upon him, during the midday heat. The Messenger of Allah, peace and blessings of Allah be upon him, said to us: "Delay the prayer until it is cooler, for the intensity of the heat is from the scorching of Hell."