Sahih Bukhari

Narrated `Abdullah bin Mas`ud:I said, ""O Allah's Messenger (ﷺ)! Which is the biggest sin?"" He said, ""To set up rivals to Allah by worshipping others though He alone has created you."" I asked, ""What is next?"" He said, ""To kill your child lest it should share your food."" I asked, ""What is next?"" He said, ""To commit illegal sexual intercourse with the wife of your neighbor