Musnad Ahmad 528:3

'Abd al-Rahman ibn Mahdi narrated to us, from Mu'awiyah—meaning Ibn Salih—from 'Abd al-Rahman ibn Jubayr, from his father, that al-Nawwas ibn Sam'an al-Ansari said—and Zayd ibn al-Hubab al-Ansari said likewise—he said: I asked the Prophet, peace and blessings of Allah be upon him, about righteousness and sin. He said: "Righteousness is good character, and sin is what wavers in your chest and you dislike that people should find out about it."