Sunan An-Nasa'i

It was narrated that 'Abdullah said:""I asked the Messenger of Allah [SAW], which sin is most grievous?"" He said: ""Shirk, setting up a rival to Allah, committing adultery with your neighbor's wife, and killing your child for fear of poverty, and that he may eat with you."" Then 'Abdullah recited the Verse: ""And those who invoke not any other Ilah (god) along with Allah