Sayyiduna Wabisah bin Ma'bad (may Allah be pleased with him), who was a Companion of the Prophet (peace and blessings be upon him), said: I asked the Messenger of Allah (peace and blessings be upon him) about righteousness and sin, and he (peace and blessings be upon him) said: "O Wabisah! You have come to ask me about righteousness and sin?" I said: Yes, by the One who sent you with the truth, that is exactly what I came to ask you about. He (peace and blessings be upon him) said: "Righteousness is that with which your heart is at ease, and sin is that which troubles your heart, even if people give you rulings about it."
Hadith Referenceالمعجم الكبير للطبراني / باب الواو / 18622