Musnad Abu Ya'la al-Mawsili 150:409

Al-Abbas ibn al-Walid narrated to us, Abu al-Ahwas narrated to us, from Ash'ath ibn Abi al-Sha'tha', from his father, from Masruq, who said: Aisha said: I asked the Messenger of Allah, peace and blessings of Allah be upon him, about looking around during prayer. He said: "It is a snatching that the devil snatches from the servant's prayer."