Musnad Ahmad 26:552

Waki’ and Abu Mu’awiyah narrated to us—the meaning being the same—they said: Al-A’mash narrated to us, from Abu Wa’il, from Abdullah, who said: A man came to the Prophet, may Allah bless him and grant him peace, and said: "Which sin is the greatest?" He said: "That you set up an equal to Allah, while He created you." He said: "Then what?" He said: "Then that you kill your child out of fear that he will eat with you." He said: "Then what?" He said: "Then that you commit adultery with the wife of your neighbor." He said: So Allah, the Mighty and Majestic, revealed the confirmation of that in His Book: {And those who do not invoke with Allah another deity} [Al-Furqan: 68] up to His saying: {And whoever does that will meet a penalty} [Al-Furqan: 68].