Sahih Muslim Book 4, Hadith Number 1024.

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 Salih al-Samman reported: I narrate to you what I heard and saw from Abu Sa’id al-Khudri: One day I was with Abu Sa’id and he was saying prayer on Friday turning to a thing which concealed him from the people when a young man from Banu Mu’ait came there and he tried to pass in front of him; he turned him back by striking his chest. He looked about but finding no other way to pass except in front of Abu Sa’id, made a second attempt. He (Abu Sa’id) turned him away by Striking his chest more vigorously than the first stroke. He stood up and had a scuffle with Abu Sa’id. Then the people gathered there He came out and went to Marwan and complained to him what had happened to him. Abu Sa’id too came to Marwan. Marwin said to him: What has happened to you and the son of your brother that he came to complain against you? Abu Sa’id said: I heard from the Messenger of Allah (may peace be upon him) saying: When any one of you prays facing something which conceals him from people and anyone tries to pass in front of him, he should be turned away, but if he refuses, he should be forcibly restrained from it, for he is a devil.