Fiqh-us-Sunnah Volume 2, Supererogatory Prayer, Fiqh 2.082.
Section : Turning to a side due to some need.
Ibn Abbas relates: “The Messenger of Allah would turn to his right and left he would not turn his head to see behind him.” This is related by Ahmad.
Abu Dawud records that when the Prophet sallallahu alehi wasallam prayed, “he looked toward a valley because he had sent some horsemen to guard the valley.”
Anas ibn Sireen says: “I saw Anas ibn Malik lift his eyes to something while he was praying.” This is related by Ahmad.