Musnad Ahmad 31:404

Ishaq narrated to us, he said: Malik informed me, from Zayd ibn Aslam, from Abd al-Rahman ibn Abi Sa'id al-Khudri, from his father, that 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 is able. If he refuses, then let him fight him, for he is only a devil."