Musnad Ahmad 594:3

Yazid ibn Harun narrated to us, Hammad ibn Salamah narrated to us, from al-Zubayr Abu Abd al-Salam, from Ayyub ibn Abd Allah ibn Makraz, from Wabisa ibn Ma'bad, who said: I came to the Messenger of Allah, peace and blessings of Allah be upon him, and I intended not to leave anything of righteousness (birr) and sin (ithm) without asking him about it. There was a gathering with him, so I went to step over the people. They said: "Move away, O Wabisa, from the Messenger of Allah, peace and blessings of Allah be upon him; move away, O Wabisa." I said: "I am Wabisa, let me draw near to him, for he is the most beloved of people to me that I should draw near to him." He said to me: "Draw near, O Wabisa; draw near, O Wabisa." So I drew near to him until my knee touched his knee. He said: "O Wabisa, shall I tell you what you came to ask me about, or will you ask me?" I said: "O Messenger of Allah, tell me." He said: "You came to ask me about righteousness and sin?" I said: "Yes." He gathered his three fingers and began to poke them into my chest, saying: "O Wabisa, consult your soul. Righteousness is what the heart finds tranquility in and the soul finds tranquility in, and sin is what wavers in the heart and fluctuates in the chest, even if the people give you a verdict and give you a verdict."