Sunan an-Nasa'i

It was narrated that 'Abdullah said: "I said: “O Messenger of Allah, which sin is the most grievous?' He said: “Setting up a rival to Allah while it is He that has created you.' I said: “Then what?' He said: “Killing your child for fear that he may eat with you.' I said: “Then what?' He said: “Committing adultery with your neighbor's wife””””””"