Sahih Bukhari, Chapter: Witnesses

The Prophet (SAW) said thrice, "Should I inform you out the greatest of the great sins?" They said, "Yes, O Allah's Apostle (SAW)!" He said, "(1)To join others in worship with Allah (2) and to be undutiful to one's parents." The Prophet (SAW) then sat up after he had been reclining (on a pillow) and said, "(3) And I warn you against giving a false witness, and he kept on saying that warning till we thought he would not stop. (See Hadith No. 7, Vol. 8)