Musannaf Ibn Abi Shayba 3:5792

'Abbad ibn al-'Awwam narrated to us, from Dawud ibn Abi Hind, from Abu Harb ibn Abi al-Aswad, that 'Ali departed from Basra and prayed the Dhuhr as four [rak'ahs]. He then said: "As for me, when we pass this hut, we will pray two rak'ahs."