Musannaf Ibn Abi Shayba 3:895

Ibn Fudayl narrated to us, from Isma'il ibn Sumay', from Muslim al-Batin, from Abu al-Bakhtari, who said: 'Ali would depart from the midday prayer (al-hajir) in the heat, then the one who was departing would set off to Quba', and he would find them praying.