Sunan An-Nasai, Chapter: The Book of Purification

that the Prophet (saw) met him in one of the streets of Al-Madinah while he was Junub, so he slipped away from him and performed Ghusl. The Prophet (saw) noticed he was not there, and when he came he said: 'Where were you, O Abu Hurairah?' He said: 'O Messenger of Allah, you met us but I was Junub, and I did not want to sit in your presence until I had performed Ghusl.' He said: 'Subhan Allah! The believer is not made impure (Najis).'" (Sahih)