Jami` at-Tirmidhi 2389
جامع الترمذي#2389SahihAn-Nawas bin Sama'an narrated that a man came asking the Messenger of Allah (s.a.w) about righteousness and sin. So the Prophet (s.a.w) said:"Righteouness is good behaviour, and sin is what fluctuates in your chest, and you would hate that the people discovered it about you
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Ahmad Muhammad ShakirSahih
Al-AlbaniSahih
Bashar Awad MaaroufHasan Sahih
Zubair Ali ZaiSahih Muslim
In-book reference: 36:86