Musannaf Ibn Abi Shayba 3:2567

Ibn ‘Uyaynah narrated to us, from al-Zuhri, from ‘Ubayd Allah, from his father, who said: I came to ‘Umar while he was praying during the midday heat. I stood to his left, so he placed me to his right. Then Yarfa’, the freed slave of ‘Umar, came, so we both stepped back behind him.