Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) said: The Messenger of Allah (peace and blessings be upon him) said: "The adulterer, at the time he commits adultery, is not a believer." Ikrimah said: I said to Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both): Then how is faith taken away? He said: "Like this" - and while describing it he interlaced his fingers, then pulled them apart - "then when he repents, faith returns to him in the same way."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 11749