It is narrated from Sayyiduna Abu Sa'id al-Khudri (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "When one of you is praying, let him not allow anyone to pass in front of him, and let him stop him as far as he can. If he insists on passing, then let him forbid him firmly, for he is only a devil."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3445