Musnad Ahmad 26:690

Waki' 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 companions of the Messenger of Allah (peace be upon him), and they said: "Which of us has not wronged himself?" The Messenger of Allah (peace be upon him) said: "It is not as you think. It is only as Luqman said to his son: 'O my son, do not associate partners with Allah; indeed, association [with Him] is a great injustice'" [Luqman: 13].