(40) باب قَوْلِ اللَّهِ تَعَالَى {فَلاَ تَجْعَلُوا لِلَّهِ أَنْدَادًا}
Narrated `Abdullah:
I asked Allah's Messenger (ﷺ) "What is the biggest sin in the sight of Allah?" He said, "To set up rivals unto Allah though He alone created you." I said, "In fact, that is a tremendous sin," and added, "What next?" He said, "To kill your son being afraid that he may share your food with you." I further asked, "What next?" He said, "To commit illegal sexual intercourse with the wife of your neighbor."
Reference: Sahih al-Bukhari 7520
In-book reference: Book 97, Hadith 145
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 9, Book 93, Hadith 611