Musnad Ahmad 1101:13

'Ali ibn 'Ayyash narrated to us, Abu 'Ubaydah al-Walid ibn Kamil, from the people of Homs, the Bajali, narrated to me, al-Muhallab ibn Hujr al-Bahrani, from Duba'ah bint al-Miqdad ibn al-Aswad, from her father, that he said: "I did not see the Messenger of Allah, peace and blessings of Allah be upon him, pray facing a pillar, nor a piece of wood, nor a tree, except that he placed it to his right eyebrow or his left, and he would not face it directly."