337.The Prophet (peace be upon him) was asked: "What is the greatest sin?" He (peace be upon him) replied, "To ascribe divinity to someone else other than Allah, when He is the One Who created you." What next?" the Prophet (peace be upon him) was asked, "To kill your child out of fear that it will share your food," he (peace be upon him) replied. (Bukhari, Muslim).
(The Lawful and Prohibited in Islam (arb: Al Halal Wal Haram Fil Islam) by. Yusuf Qaradawi).