Narrated `Abdullah (RA) : I asked Allah’s Messenger (Peace Be Upon Him) “What is the biggest sin in the sight of Allah?” He (Peace Be Upon Him) 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 (Peace Be Upon Him) said, “To kill your son being afraid that he may share your food with you.” I further asked, “What next?” He(Peace Be Upon Him) said, “To commit illegal sexual intercourse with the wife of your neighbor.”
SAHIH BUKHARI
Vol. 9, Book 93, Hadith 611
