Sunnah.com reference : Book 2, Hadith 127English translation : Book 2, Hadith 253Arabic reference : Book 2, Hadith 255
Narrated [Abu Hurairah (RA)]:
Umar came over Hassan while reciting poetry inside the mosque and looked at him sternly, then he (Hassan) said: "I used to recite poetry inside it (the mosque) in the presence of one who is more pious than you [i.e. the Prophet (ﷺ)]".

[Agreed upon].
وَعَنْهُ ‏- رضى الله عنه ‏- { أَنَّ عُمَرَ ‏- رضى الله عنه ‏- مُرَّ بِحَسَّانَ يَنْشُدُ فِي اَلْمَسْجِدِ , فَلَحَظَ إِلَيْهِ , فَقَالَ : "قَدْ كُنْتُ أَنْشُدُ , وَفِيهِ مَنْ هُوَ خَيْرٌ مِنْكَ }  .‏ مُتَّفَقٌ عَلَيْهِ .‏  1‏‏1 ‏- صحيح .‏ رواه البخاري (3212)‏ ، ومسلم (2485)‏ .‏