Sahih Bukhari Volume 4, Book 55, Hadith Number 580.
Narated By Abdullah : When the Verse: “It is those who believe and do not confuse their belief with wrong (i.e. joining others in worship with Allah” (6.83) was revealed, we said, “O Allah’s Apostle! Who is there amongst us who has not done wrong to himself?” He replied, “It is not as you say, for ‘wrong’ in the Verse and ‘do not confuse their belief, with wrong means ‘SHIRK’ (i.e. joining others in worship with Allah). Haven’t you heard Luqman’s saying to his son, ‘O my son! Join not others in worship with Allah, verily joining others in worship with Allah is a great wrong indeed.” (31.13)