Sahih Bukhari Volume 001, Book 005, Hadith Number 281.
Narated By Abu Huraira : The Prophet came across me in one of the streets of Medina and at that time I was Junub. So I slipped away from him and went to take a bath. On my return the Prophet said, "O Abu Huraira! Where have you been?" I replied, "I was Junub, so I disliked to sit in your company." The Prophet said, "Subhan Allah! A believer never becomes impure."