It was narrated that Ibn 'Abbas said: "The Messenger of Allah said: “No one who commits Zina is a believer at the moment when he is committing Zina, and no one who drinks wine is a believer at the moment when he is drinking it, and no thief is a believer at the moment when he is stealing, and no killer is a believer at the moment he is killing”"
SahihSahihSahih BukhariBook 45 · Hadith 164