Musnad Ahmad 26:42

Abu Mu'awiyah narrated to us, al-A'mash narrated to us, from Ibrahim, from 'Alqamah, from 'Abdullah, who said: When this verse was revealed: "Those who believe and do not mix their belief with injustice" [al-An'am: 82], it was difficult for the people, and they said: "O Messenger of Allah, which of us does not wrong his own soul?" He said: "It is not what you mean. Have you not heard what the righteous servant said: 'O my son, do not associate partners with Allah; indeed, association [with Him] is a great injustice' [Luqman: 13]? It is only shirk (polytheism)."