Sahih Bukhari Volume 8, Book 81, Hadith Number 763.

Narrated By Abu Huraira : Allah’s Apostle said, “When an adulterer commits illegal sexual intercourse, then he is not a believer at the time he is doing it; and when somebody drinks an alcoholic drink, then he is not believer at the time of drinking, and when a thief steals, he is not a believer at the time when he is stealing; and when a robber robs and the people look at him, then he is not a believer at the time of doing it.” Abu Huraira in another narration, narrated the same from the Prophet with the exclusion of robbery.