The sin of the person who recites the Qur'an to show off or to gain some worldly benefit, or to feel proud etc.
حَدَّثَنَا عَبْدُ اللَّهِ بْنُ يُوسُفَ، أَخْبَرَنَا مَالِكٌ، عَنْ يَحْيَى بْنِ سَعِيدٍ، عَنْ مُحَمَّدِ بْنِ إِبْرَاهِيمَ بْنِ الْحَارِثِ التَّيْمِيِّ، عَنْ أَبِي سَلَمَةَ بْنِ عَبْدِ الرَّحْمَنِ، عَنْ أَبِي سَعِيدٍ الْخُدْرِيِّ ـ رضى الله عنه ـ أَنَّهُ قَالَ سَمِعْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يَقُولُ " يَخْرُجُ فِيكُمْ قَوْمٌ تَحْقِرُونَ صَلاَتَكُمْ مَعَ صَلاَتِهِمْ، وَصِيَامَكُمْ مَعَ صِيَامِهِمْ، وَعَمَلَكُمْ مَعَ عَمَلِهِمْ، وَيَقْرَءُونَ الْقُرْآنَ لاَ يُجَاوِزُ حَنَاجِرَهُمْ، يَمْرُقُونَ مِنَ الدِّينَ كَمَا يَمْرُقُ السَّهْمُ مِنَ الرَّمِيَّةِ، يَنْظُرُ فِي النَّصْلِ فَلاَ يَرَى شَيْئًا، وَيَنْظُرُ فِي الْقِدْحِ فَلاَ يَرَى شَيْئًا، وَيَنْظُرُ فِي الرِّيشِ فَلاَ يَرَى شَيْئًا، وَيَتَمَارَى فِي الْفُوقِ ".
Narrated Abu Sa`id Al-Khudri: I heard Allah's Messenger (ﷺ) saying, "There will appear some people among you whose prayer will make you look down upon yours, and whose fasting will make you look down upon yours, but they will recite the Qur'an which will not exceed their throats (they will not act on it) and they will go out of Islam as an arrow goes out through the game whereupon the archer would examine the arrowhead but see nothing, and look at the unfeathered arrow but see nothing, and look at the arrow feathers but see nothing, and finally he suspects to find something in the lower part of the arrow."