Sahih al-Bukhari 4629
Narrated `Abdullah:
When:"...and confuse not their belief with wrong." (6.82) was revealed, the Prophet's companions 
said, "Which of us has not done wrong?" Then there was revealed:-- "Verily joining others in worship 
with Allah is a tremendous wrong indeed." (31.13)
حَدَّثَنِي مُحَمَّدُ بْنُ بَشَّارٍ، حَدَّثَنَا ابْنُ أَبِي عَدِيٍّ، عَنْ شُعْبَةَ، عَنْ سُلَيْمَانَ، عَنْ إِبْرَاهِيمَ، عَنْ عَلْقَمَةَ، عَنْ عَبْدِ اللَّهِ ـ رضى الله عنه ـ قَالَ لَمَّا نَزَلَتْ ‏{‏وَلَمْ يَلْبِسُوا إِيمَانَهُمْ بِظُلْمٍ‏}‏ قَالَ أَصْحَابُهُ وَأَيُّنَا لَمْ يَظْلِمْ فَنَزَلَتْ ‏{‏إِنَّ الشِّرْكَ لَظُلْمٌ عَظِيمٌ‏}‏