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 مُسَدَّدٌ، حَدَّثَنَا يَحْيَى، عَنْ شُعْبَةَ، عَنْ قَتَادَةَ، عَنْ أَنَسِ بْنِ مَالِكٍ، عَنْ أَبِي مُوسَى، عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ " الْمُؤْمِنُ الَّذِي يَقْرَأُ الْقُرْآنَ وَيَعْمَلُ بِهِ كَالأُتْرُجَّةِ، طَعْمُهَا طَيِّبٌ وَرِيحُهَا طَيِّبٌ، وَالْمُؤْمِنُ الَّذِي لاَ يَقْرَأُ الْقُرْآنَ وَيَعْمَلُ بِهِ كَالتَّمْرَةِ، طَعْمُهَا طَيِّبٌ وَلاَ رِيحَ لَهَا، وَمَثَلُ الْمُنَافِقِ الَّذِي يَقْرَأُ الْقُرْآنَ كَالرَّيْحَانَةِ، رِيحُهَا طَيِّبٌ وَطَعْمُهَا مُرٌّ، وَمَثَلُ الْمُنَافِقِ الَّذِي لاَ يَقْرَأُ الْقُرْآنَ كَالْحَنْظَلَةِ، طَعْمُهَا مُرٌّ ـ أَوْ خَبِيثٌ ـ وَرِيحُهَا مُرٌّ ".
Narrated Abu Musa: The Prophet (ﷺ) said, "The example of a believer who recites the Qur'an and acts on it, like a citron which tastes nice and smells nice. And the example of a believer who does not recite the Qur'an but acts on it, is like a date which tastes good but has no smell. And the example of a hypocrite who recites the Qur'an is like a Raihana (sweet basil) which smells good but tastes bitter And the example of a hypocrite who does not recite the Qur'an is like a colocynth which tastes bitter and has a bad smell."