Sahih Bukhari

Narrated `Abdullah:I said 'O Allah's Messenger (ﷺ)! Which sin is the greatest?"" He said, ""To set up a rival unto Allah, though He Alone created you."" I said, ""What next?"" He said, ""To kill your son lest he should share your food with you."" I further asked, ""What next?"" He said, ""To commit illegal sexual intercourse with the wife of your neighbor."" And then Allah revealed as proof of the statement of the Prophet: 'Those who invoke not with Allah any other god)................. (to end of verse)