It is narrated from Sayyiduna Abu Hurairah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "No person can commit a major theft of something valuable, towards which people's eyes are set, while remaining a believer; and if he is committing theft, then in that state he does not remain a believer."
Hadith Referenceسنن دارمي / من كتاب الاضاحي / 2033
Hadith Takhrijاس روایت کی سند صحیح اور حدیث متفق علیہ ہے۔ دیکھئے: [بخاري 2475] ، [مسلم 57] ، [نسائي 5676] ، [ابن ماجه 3936] ، [أبويعلی 2699] ، [ابن حبان 186] ، [الحميدي 1163]
Brief Explanation
(Commentary on Hadith 2032)
That is, at the time of committing such a crime, he does not remain a believer; faith departs from him. If faith had remained, why would he commit such an act?
From this hadith, it is understood that the one who commits plunder, theft, or robbery—if these people claim to be Muslims, then they are utterly false in their claim. The characteristic of a Muslim is that if he happens to commit theft, adultery, or any other evil deed, he becomes extremely remorseful, repents forever, and remains engaged in seeking forgiveness (istighfar).