Allah's Messenger (ﷺ) said thrice, "Shall I not inform you of the biggest of the great sins?" We said, "Yes, O Allah's Messenger (ﷺ)" He said, "To join partners in worship with Allah: to be undutiful to one's parents." The Prophet (ﷺ) sat up after he had been reclining and added, "And I warn you against giving forged statement and a false witness; I warn you against giving a forged statement and a false witness." The Prophet kept on saying that warning till we thought that he would not stop.