It is narrated from Abu Ja'far that he was asked about the statement of the Messenger of Allah, peace and blessings be upon him: "A fornicator cannot commit fornication while remaining a believer, and a thief cannot steal while remaining a believer." So Abu Ja'far said: This is Islam, and he drew a large circle. This is faith, and he drew a small circle in the middle of the large circle, and said: Faith is confined within Islam. So when he commits fornication and theft, he comes out from faith to Islam, and only disbelief in the essence of Allah can expel him from Islam.
Hadith Referenceمسند اسحاق بن راهويه / كتاب الايمان / 58
Hadith Takhrij«السنة لعبد اللفه بن احمد : 342/1 . شرح اصول اعتقاد اهل السنة والجماعة للاكائي6 ، رقم : 1877 . قوت القلوب لابي طالب المكي : 221/2»