Sahih Bukhari Volume 001, Book 002, Hadith Number 031.
Narated By 'Abdullah : When the following Verse was revealed: "It is those who believe and confuse not their belief with wrong (worshipping others besides Allah.)" (6:83), the companions of Allah's Apostle asked, "Who is amongst us who had not done injustice (wrong)?" Allah revealed: "No doubt, joining others in worship with Allah is a great injustice (wrong) indeed." (31.13)