جامع الترمذي

Narrated 'Abdullah: "I asked the Messenger of Allah (ﷺ) which sin is the worst.' He said: 'That you make an equal to Allah while it is He who created you, that you kill your child so that he not eat with you - or because of your food, that you commit adultery with your neighbor's wife.'" He said: "And he recited this Ayah: 'And those who invoke not any other god along with Allah, nor kill such life as Allah has forbidden, except for what is required, nor commit illegal sexual intercourse - and whoever does that shall receive punishment. The torment will be doubled for him on the Day of Resurrection, and he will abide therein in disgrace (25:68 & 69).'"