Sahih Bukhari
Punishment of Disbelievers at War with Allah and His Apostle
Volume: 008 / Book Number: 082 / Hadith Number: 801
Narrated 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."