Musannaf Ibn Abi Shayba 3:5125

Muhammad ibn Yazid narrated to us, from Ayyub, from Abu al-Ala, from Mu’awiyah ibn Qurrah, from his father, who said: Umar saw me while I was praying between two pillars, so he took hold of the back of my neck and brought me near to a sutrah (barrier). He said: "Pray towards it."