Musnad Abu Ya'la al-Mawsili 150:130

Abu Ya'la Ahmad ibn Ali ibn al-Muthanna al-Mawsili informed us, Abd al-A'la narrated to us, Abd 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, may Allah bless him and grant him peace, about looking around during prayer. He said: "It is a snatching that the devil snatches from the servant's prayer."