Sahih Bukhari
Prophetic Commentary on the Quran (Tafseer of the Prophet (PBUH))
Volume: 006 / Book Number: 060 / Hadith Number: 284
Narrated 'Abdullah:
I or somebody, asked Allah's Apostle "Which is the biggest sin in the Sight of Allah?" He said, "That you set up a rival (in worship) to Allah though He Alone created you." I asked, "What is next?" He said, "Then, that you kill your son, being afraid that he may share your meals with you." I asked, "What is next?" He said, "That you commit illegal sexual intercourse with the wife of your neighbor." Then the following Verse was revealed to confirm the statement of Allah's Apostle:
"Those who invoke not with Allah, any other god, nor kill life as Allah has forbidden except for just cause, nor commit illegal sexual intercourse." (25.68)