Musnad Ahmad 3:124

'Abdullah narrated to us, Suwayd ibn Sa'id narrated to us, Ibrahim ibn Sa'd narrated to us, my father narrated to me, from his father, who said: I was praying, and a man passed in front of me, so I prevented him, but he refused. I asked 'Uthman ibn 'Affan, and he said: "It does not harm you, O son of my brother."