It is narrated from Sayyiduna Ibn Amr (may Allah be pleased with him) that once the Noble Prophet (peace and blessings be upon him) said: "Do you know who is a Muslim?" The companions (may Allah be pleased with them) replied, "Allah and His Messenger know best." He said: "A Muslim is the one from whose tongue and hand other Muslims are safe." Then he asked, "Do you know who is a believer?" The companions (may Allah be pleased with them) replied, "Allah and His Messenger know best." He said: "A believer is the one from whom the lives and wealth of other believers are safe. And the real emigrant is the one who abandons sins and refrains from them."
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 6925