Musnad Ahmad 31:309

I read to Abd al-Rahman: Malik, from Zayd ibn Aslam, from Abd al-Rahman ibn Abi Sa'id, from Abu Sa'id al-Khudri, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "When one of you is praying, let him not allow anyone to pass in front of him, and let him repel him as much as he can. If he refuses, then let him fight him, for he is only a devil."