Musnad Ahmad 1153:729

Abu Sa’id narrated to us, he said: Za’idah narrated to us, he said: Ash’ath ibn Abi al-Sha’tha’ al-Muharibi narrated to us, from his father, from Masruq, from ‘Aishah, she said: I asked the Prophet, 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."