Sahih Muslim Book 4, Hadith Number 1023.

Chapter : The excellence of the prayer and the way it is begun and the excellence of Ruku’ and moderation in it and prostration and moderation in it, etc.

Abu Sa’id al-Khudri reported that the Messenger of Allah (may peace be upon him) said: When any one of you prays he should not let anyone pass in front of him (if there is no sutra), and should try to turn him away as far as possible, but if he refuses to go, he should turn him away forcibly for he is a devil.