Sahih Bukhari Volume 8, Book 82, Hadith Number 801.

Narrated By Abu Huraira : The Prophet said, “The one who commits an illegal sexual intercourse is not a believer at the time of committing illegal sexual intercourse and a thief is not a believer at the time of committing theft and a drinker of alcoholic drink is not a believer at the time of drinking. Yet, (the gate of) repentance is open thereafter.”