Musnad Ahmad 528:4

'Abd al-Quddus Abu al-Mughirah al-Khawlani narrated to us, he said: Safwan—meaning Ibn 'Amr—narrated to us, Yahya ibn Jabir al-Qass narrated to us, from al-Nawwas ibn Sam'an, who said: I asked the Messenger of Allah, peace and blessings of Allah be upon him, about righteousness and sin. He said: "Righteousness is good character, and sin is what pricks at your soul and you dislike that people should come to know of it."