Musnad Ahmad 941:50

Yazid narrated to us, Ibn Abi Dhi’b narrated to us, from al-Zibriqan: A group of Quraysh were gathered when Zayd ibn Thabit passed by them. They sent two of their young servants to him to ask him about the middle prayer. He said: "It is the Asr prayer." Then two men from among them stood up and asked him, and he said: "It is the Dhuhr prayer." They then went to Usamah ibn Zayd and asked him, and he said: "It is the Dhuhr prayer. The Messenger of Allah (peace and blessings of Allah be upon him) used to pray Dhuhr in the midday heat, and there would be no one behind him except one or two rows of people, as they were in their midday rest and their trade." Then Allah the Exalted revealed: "Guard strictly the (five obligatory) prayers, especially the middle prayer, and stand before Allah with obedience" [Al-Baqarah: 238]. He said: The Messenger of Allah (peace and blessings of Allah be upon him) then said: "Men must certainly desist, or I will surely burn down their houses."