Musnad Ahmad 26:581

'Abd al-Rahman narrated to us, from Sufyan, from Mansur, and al-A'mash, and Wasil, from Abu Wa'il, from 'Amr ibn Sharhabil, from 'Abdullah, who said: I said: "O Messenger of Allah, which sin is the greatest in the sight of Allah, the Almighty and Majestic?" He said: "That you set up a rival to Allah, the Almighty and Majestic, while He created you." I said: "Then what?" He said: "Then that you kill your child out of fear that he might eat from your food" — and 'Abd al-Rahman said once: "that he might eat with you." He said: Then I said: "Then what?" He said: "That you commit adultery with the wife of your neighbor."