عَنِ النَّوَّاسِ بْنِ سَمْعَانَ الْأَنْصَارِيِّ رَضِيَ اللَّهُ عَنْهُ إِنَّهُ سَأَلَ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَآلِهِ وَسَلَّمَ عَنِ الْبِرِّ وَالْإِثْمِ فَقَالَ الْبِرُّ حُسْنُ الْخُلُقِ وَالْإِثْمُ مَا حَاكَ فِي صَدْرِكَ وَكَرِهْتَ أَنْ يَطَّلِعَ النَّاسُ عَلَيْهِ
It is narrated from Sayyiduna Nawwas bin Sam'an (may Allah be pleased with him) that he asked the Messenger of Allah (peace and blessings be upon him) about virtue and sin, and the Prophet (peace and blessings be upon him) replied to him: Virtue is good character, and sin is that which pricks your heart and you dislike that people become aware of it.