Musnad Ahmad 26:65

Abu Mu'awiyah narrated to us, Al-A'mash narrated to us, from Shaqiq, from Abdullah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) was asked: "Which sin is the greatest?" He said: "That you set up a rival to Allah, while He created you." He said: "Then what?" He said: "That you kill your child out of fear that he will eat with you." He said: "Then what?" He said: "That you commit adultery with the wife of your neighbor." Abdullah said: "Then Allah revealed the confirmation of that: 'And those who do not invoke with Allah another deity or kill the soul which Allah has forbidden, except by right, and do not commit unlawful sexual intercourse. And whoever should do that will meet a penalty.'" [Al-Furqan: 68]