Musannaf Ibn Abi Shayba 3:912

Abu Bakr narrated to us, he said: Muhammad ibn Fudayl narrated to us, from Abu Malik al-Ashja‘i, from Kathir ibn Mudrik, from al-Aswad ibn Yazid, who said: Abdullah said: "The beginning of the time for Dhuhr is that you look at your feet and measure three feet to five feet. And the beginning of the latter time is five feet to seven feet." I think he said: "In the winter."