Verily, what I fear for you is a man who recites the Qur’an until its brightness appears on him and he becomes a support of Islam. (This continues) until this man changes his state to what Allah wills. He detaches himself from it and throws it behind his back. Then he starts attacking his neighbor with the sword, accusing him of polytheism

عن حذيفة رضي الله عنه قال: قال رسول الله صلى الله عليه وسلم : «إنَّ ما أَتَخوَّفُ عليكم رجلٌ قَرَأ القرآنَ حتى إذا رُئِيَتْ بَهْجتُه عليه، وكان رِدْئًا للإِسلام، غَيَّرَه إلى ما شاء الله، فانْسَلَخَ مِنْه ونَبَذَه وراءَ ظَهْرِه، وسَعَى على جاره بالسَّيف، ورمَاه بالشِّرك»، قال: قلتُ: يا نبيَّ الله، أيُّهما أوْلى بالشِّرك، المَرْمِي أم الرَّامي؟ قال: «بل الرَّامي».

Hudhayfah (may Allah be pleased with him) reported that the Messenger of Allah (may Allah's peace and blessings be upon him) said: "Verily, what I fear for you is a man who recites the Qur’an until its brightness appears on him and he becomes a support of Islam. (This continues) until this man changes his state to what Allah wills. He detaches himself from it and throws it behind his back. Then he starts attacking his neighbor with the sword, accusing him of polytheism." I asked: "O Prophet, which of the two deserves more to be described as a polytheist? The accused or the accuser?" He replied: "The accuser."

Source · Narrated by Ibn Hebban

From the Hadith Encyclopedia (hadeethenc.com).