Sahih Bukhari
Limits and Punishments set by Allah (Hudood)
Volume: 008 / Book Number: 081 / Hadith Number: 773
Narrated Ibn 'Abbas:
The Prophet said, "When (a person) an adulterer commits illegal sexual intercourse then he is not a believer at the time he is doing it; and when somebody steals, then he is not a believer at the time he is stealing."