BUKHARI 4.495: (cf. 3.505B and 6.530)

Abu Said Al-Khudri narrated: 

The Prophet said, "If while you are praying, somebody intends to pass in front of you, prevent him; and should he insist, prevent him again; and if he insists again, fight with him (i.e. prevent him violently e.g. pushing him violently), because such a person is a devil."