Musannaf Ibn Abi Shayba 3:739

Ya'la ibn 'Ubayd narrated to us, from Yahya ibn Sa'id, from Muhammad ibn Yahya ibn Habban, from his paternal uncle Wasi' ibn Habban, who said: I was praying, and Ibn 'Umar was leaning his back against the wall of the qibla. I turned away to my left. He said, "What prevents you from turning away to your right?" I said, "Nothing, except that I saw you, so I turned toward you." He said, "You did correctly. People say you should turn away to your right, but if you are praying, turn away—if you wish—to your right or to your left."